portico: Auto-detect field to focus for registration page.
portico: Auto-detect field to focus for registration page.

This replaces the manually-curated logic for which field to focus.

hackerkid/zulip,eeshangarg/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,synicalsyntax/zulip,rht/zulip,timabbott/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,jackrzhang/zulip,rishig/zulip,shubhamdhama/zulip,rishig/zulip,eeshangarg/zulip,synicalsyntax/zulip,synicalsyntax/zulip,zulip/zulip,shubhamdhama/zulip,timabbott/zulip,shubhamdhama/zulip,synicalsyntax/zulip,timabbott/zulip,zulip/zulip,zulip/zulip,shubhamdhama/zulip,andersk/zulip,rishig/zulip,brainwane/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,showell/zulip,brainwane/zulip,dhcrzf/zulip,andersk/zulip,timabbott/zulip,dhcrzf/zulip,rht/zulip,rishig/zulip,rht/zulip,hackerkid/zulip,rishig/zulip,dhcrzf/zulip,shubhamdhama/zulip,punchagan/zulip,tommyip/zulip,punchagan/zulip,andersk/zulip,punchagan/zulip,jackrzhang/zulip,dhcrzf/zulip,synicalsyntax/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,brainwane/zulip,timabbott/zulip,dhcrzf/zulip,zulip/zulip,andersk/zulip,jackrzhang/zulip,dhcrzf/zulip,timabbott/zulip,tommyip/zulip,eeshangarg/zulip,jackrzhang/zulip,showell/zulip,punchagan/zulip,eeshangarg/zulip,tommyip/zulip,jackrzhang/zulip,hackerkid/zulip,kou/zulip,zulip/zulip,rht/zulip,jackrzhang/zulip,jackrzhang/zulip,kou/zulip,tommyip/zulip,eeshangarg/zulip,andersk/zulip,shubhamdhama/zulip,showell/zulip,tommyip/zulip,brainwane/zulip,brainwane/zulip,punchagan/zulip,dhcrzf/zulip,punchagan/zulip,showell/zulip,timabbott/zulip,showell/zulip,showell/zulip,tommyip/zulip,tommyip/zulip,kou/zulip,shubhamdhama/zulip,brainwane/zulip,kou/zulip,synicalsyntax/zulip,rishig/zulip,kou/zulip,synicalsyntax/zulip,rishig/zulip,showell/zulip,rht/zulip,brainwane/zulip,andersk/zulip,andersk/zulip