Add the nocrop option to the image pick activity

This should help avoid OOM errors in FxOS 1.3 until we can make no crop the default.
See https://bugzilla.mozilla.org/show_bug.cgi?id=959430

Note that I have not tested this pull request.  (Sorry!)
Merge pull request #45 from davidflanagan/patch-1

Add the nocrop option to the image pick activity