Add Map#remove

This is a minimal implementation; it only unbinds events
and deletes the _leaflet flag from the container.

Refs #1101.
Force touch support off for PhantomJS

PhantomJS has `'ontouchstart' in document.documentElement`, but
doesn't actually support touch.

http://code.google.com/p/phantomjs/issues/detail?id=375
https://github.com/ariya/phantomjs/pull/408
https://github.com/Leaflet/Leaflet/pull/1434#issuecomment-13843151
Merge pull request #1434 from jfirebaugh/remove

Add Map#remove