ui/fix: add link validation option to medium-editor (fixes SD-4554)
ui/fix: add link validation option to medium-editor (fixes SD-4554)

After this PR, whenever adding an anchor link using the `#` button in
the toolbar, the `http://` protocol will be automatically appended when
deemed necessary. Also fixes
[SD-4545](https://dev.sourcefabric.org/browse/SD-4545).

mdhaman/superdesk-client-core,mscam/superdesk-client-core,marwoodandrew/superdesk-client-core,superdesk/superdesk-client-core,fritzSF/superdesk-client-core,thnkloud9/superdesk-client-core,petrjasek/superdesk-client-core,mscam/superdesk-client-core,Aca-jov/superdesk-client-core,petrjasek/superdesk-client-core,lnogues/superdesk-client-core,lnogues/superdesk-client-core,mugurrus/superdesk-client-core,mscam/superdesk-client-core,pavlovicnemanja/superdesk-client-core,Aca-jov/superdesk-client-core,jerome-poisson/superdesk-client-core,pavlovicnemanja/superdesk-client-core,ioanpocol/superdesk-client-core,mscam/superdesk-client-core,Aca-jov/superdesk-client-core,jerome-poisson/superdesk-client-core,marwoodandrew/superdesk-client-core,darconny/superdesk-client-core,marwoodandrew/superdesk-client-core,thnkloud9/superdesk-client-core,marwoodandrew/superdesk-client-core,petrjasek/superdesk-client-core,superdesk/superdesk-client-core,gbbr/superdesk-client-core,thnkloud9/superdesk-client-core,darconny/superdesk-client-core,mdhaman/superdesk-client-core,superdesk/superdesk-client-core,pavlovicnemanja/superdesk-client-core,darconny/superdesk-client-core,gbbr/superdesk-client-core,ioanpocol/superdesk-client-core,mdhaman/superdesk-client-core,thnkloud9/superdesk-client-core,ioanpocol/superdesk-client-core,mugurrus/superdesk-client-core,marwoodandrew/superdesk-client-core,fritzSF/superdesk-client-core,petrjasek/superdesk-client-core,jerome-poisson/superdesk-client-core,mugurrus/superdesk-client-core,jerome-poisson/superdesk-client-core,ioanpocol/superdesk-client-core,fritzSF/superdesk-client-core,petrjasek/superdesk-client-core,fritzSF/superdesk-client-core,pavlovicnemanja/superdesk-client-core,gbbr/superdesk-client-core,jerome-poisson/superdesk-client-core,ioanpocol/superdesk-client-core,mugurrus/superdesk-client-core,gbbr/superdesk-client-core,superdesk/superdesk-client-core,lnogues/superdesk-client-core,pavlovicnemanja/superdesk-client-core,superdesk/superdesk-client-core,Aca-jov/superdesk-client-core,mdhaman/superdesk-client-core,mdhaman/superdesk-client-core,lnogues/superdesk-client-core,darconny/superdesk-client-core