Disable select2 for all multi-select inputs.
These have been nothing but trouble (they have been disabled some places) and are awkward in those places that have not been changed.

Is there any place in Galaxy where multi-select inputs + select2 are being used to create a desirable UX? If yes, can we just create a class for these particular widgets and target it with a boolean expression on the same line?
Merged in jmchilton/galaxy-central-fork-1 (pull request #379)

Disable select2 for all multi-select inputs.