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
No, that's definitely the right form. `IE8-IE11+` suggests that the behavior was introduced in IE8, `IE<11+` suggests that the behavior exists as far back as we cared to check and still exists as of IE11 and presumably beyond.