template: @template_args decorator addition

* Adds new decorator to allow overwritting template context functions by
  endpoint.  (closes #2009)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
general: defaultdict fix

* Replaces defaultdict with collections.defaultdict.  (addresses #2030)

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
messages: require.js messages

* Refactors the messages/add template to use require.js.

* Loads jQuery UI modules individually.

* Fixes the jquery timepicker add-on shim.

* Moves bootstrap.js back into jquery bundle.

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>