Misc: Drop support for older browsers; update support comments

That includes IE<8, Opera 12.x, Firefox<29, Safari<6.0 and some hacks
for old Blackberry.

Fixes gh-1836
Fixes gh-1701
Refs gh-1815
Refs gh-1820
Since we're in the neighborhood: `Support: IE10` or `Support: IE10+` or `Support: IE10-11+` (indeterminate from context)