Add angular-scroll to Gruntfile

Addendum to #229
Fix treebankPersister spec for promise callback

Addendum to #230
Fix revealToggle spec

Addendum to #229
Add option to revealToggle to always reveal

Sometimes we don't want such a button to toggle the target, but just to
show it.

Addendum to #229
Merge pull request #231 from latin-language-toolkit/spec_fixes

Addenda to #229 and #230