Update layout
Update layout

- Use placeholders rather than mixins
- Rename page content block to #content so the skiplink from the govuk
template works
- Remove display:block from content, this is set by the govuk template
assuming <main id=“content”>

joelanman/govuk_prototype_kit,nhsalpha/nhs_prototype_kit,rivalee/local-gov-links,joelanman/govuk_prototype_kit,hannalaakso/accessible-timeout-warning,glancyea/tagtest,bencullimore/nhsers,jamesarice/DPSS,PurpleBooth/govuk_prototype_kit,timpaul/ur_panel_prototype,mharrington/nhs_prototype_kit,paulpod/invgov,chrishanes/pvb_prisoner_proto,kenmaddison-scc/verify-local-patterns,BucksCountyCouncil/verify-local-patterns,nhsbsa/ppc-prototype,joelanman/govuk_prototype_kit,quis/notify-public-research-prototype,abbott567/govuk_prototype_kit,quis/notify-public-research-prototype,antimega/cites-prototype,davedark/proto-timeline,glancyea/tagtest,bencullimore/nhsers,quis/notify-public-research-prototype,timpaul/ur_panel_prototype,danblundell/verify-local-patterns,arminio/govuk_prototype_kit,antimega/cites-prototype,BucksCountyCouncil/verify-local-patterns,bencullimore/nhsers,UKHomeOffice/ReportTerroristMaterialPrototype,st3v3nhunt/prototype-ers,companieshouse/ch-accounts-prototype,abbott567/govuk_prototype_kit,danblundell/verify-local-patterns,chrishanes/pvb_prisoner_proto,dwpdigitaltech/ejs-prototype,OrcaTom/dwp_contentpatterns,timpaul/govuk_transaction_prototype_kit,gup-dwp/pip-prototype-v2,abbott567/govuk_prototype_kit,samwake/hoddat-cofc-caseworking,st3v3nhunt/prototype-ers,paulpod/invgov,tsmorgan/marx,DilwoarH/GDS-Prototype-DM-SavedSearch,mikieet/sm-prototype,karlparton/my-govuk,dwpdigitaltech/hrt-prototype,danblundell/verify-local-patterns,timpaul/GOVUKCountrySelector,dwp-rti-prototype/rti-ux-new-prototype,arminio/govuk_prototype_kit,nhsbsa/ppc-prototype,benjeffreys/hmcts-idam-proto,timpaul/govuk_transaction_prototype_kit,davedark/proto-timeline,alphagov/govuk_prototype_kit,timpaul/GOVUKCountrySelector,dwpdigitaltech/ejs-prototype,rivalee/licensing-prototype,alphagov/govuk_prototype_kit,bencullimore/nhsers,LandRegistry/dmp-prototype,st3v3nhunt/prototype-ers,tsmorgan/marx,tsmorgan/jsa-complaints,OrcaTom/dwp_contentpatterns,benjeffreys/hmcts-idam-proto,alphagov/govuk_prototype_kit,karlparton/my-govuk,timpaul/nhs_prototype_kit,gavinwye/govuk_prototype_kit,mikieet/sm-prototype,hannalaakso/accessible-timeout-warning,kenmaddison-scc/verify-local-patterns,mikieet/sm-3,mikieet/sm-3,st3v3nhunt/prototype-ers,dwpdigitaltech/hrt-prototype,Demwunz/esif-prototype,Demwunz/esif-prototype,samwake/hoddat-cofc-caseworking,nhsbsa/ppc-prototype,dwpdigitaltech/digital-debt,dwpdigitaltech/digital-debt,gavinwye/govuk_prototype_kit,hannalaakso/accessible-timeout-warning,mharrington/nhs_prototype_kit,chrishanes/pvb_prisoner_proto,kenmaddison-scc/verify-local-patterns,samwake/hoddat-cofc-caseworking,jeremygillies-ea/data_returns_prototype,Demwunz/esif-prototype,rivalee/licensing-prototype,timpaul/nhs_prototype_kit,jamesarice/DPSS,OrcaTom/dwp_contentpatterns,nhsalpha/nhs_prototype_kit,LandRegistry/dmp-prototype,DilwoarH/GDS-Prototype-DM-SavedSearch,nhsalpha/nhs_prototype_kit,joelanman/govuk_transaction_prototype_kit,karlparton/my-govuk,dwp-rti-prototype/rti-ux-new-prototype,paulpod/invgov,dwp-rti-prototype/rti-ux-new-prototype,dwpdigitaltech/hrt-prototype,mharrington/nhs_prototype_kit,arminio/govuk_prototype_kit,gup-dwp/pip-prototype-v2,rivalee/local-gov-links,BucksCountyCouncil/verify-local-patterns,timpaul/nh_prototype_kit,joelanman/govuk_transaction_prototype_kit,companieshouse/ch-accounts-prototype,timpaul/registers-hackday,LandRegistry/dmp-prototype,jeremygillies-ea/data_returns_prototype,DilwoarH/GDS-Prototype-DM-SavedSearch,dwpdigitaltech/digital-debt,benjeffreys/hmcts-idam-proto,antimega/performance-self-serve-prototype,UKHomeOffice/ReportTerroristMaterialPrototype,jeremygillies-ea/data_returns_prototype,glancyea/tagtest,timpaul/registers-hackday,timpaul/nh_prototype_kit,PurpleBooth/govuk_prototype_kit,gup-dwp/pip-prototype-v2,tsmorgan/marx,nhsalpha/nhs_prototype_kit,davedark/proto-timeline,dwpdigitaltech/ejs-prototype,antimega/performance-self-serve-prototype,tsmorgan/jsa-complaints