settings: Add some visual weight to the section headings.
settings: Add some visual weight to the section headings.

I've found this file hard to navigate for a while.  We actually have a
little hierarchy of section headings which applies to a lot of the
file already; make the boundaries bolder.

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