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
I don't think you'd ever use `// Support: IE` because it would imply you knew what future IE versions did. The comment should indicate the last version you tested so someone can come along later and determine whether a newer version fixed it. 

Of course this is complicated because lately Microsoft has been slipstreaming fixes into IE11, but I don't know that any of those include patches we've addressed.