base: navigation menu buttons cleanup

* Removes inline javascript and css.

* Adds `navbar-btn` class to login and register buttons.

Signed-off-by: Harris Tzovanakis <me@drjova.com>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
assets: requirejs exclude option

* Adds support for exclusion of files in RequireJS builds, to prevent
  files from being included multiple times. (closes #2411)

* Enables more aggressive compression for UglifyJS.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
base: requirejs improvements

* Several improvements for better requirejs compliance.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
deposit: datetime picker library modification

* Changes the datetime picker library from the jQuery UI to
  bootstrap-datetimepicker.

* Increases the consistency with the Bootstrap design.

* NOTE introduces new JS library
  <https://github.com/Eonasdan/bootstrap-datetimepicker>.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Co-authored-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
Co-authored-by: Javier Martin Montull <javier.martin.montull@cern.ch>