workflows: further update JavaScript
- Refactors the way URLs are passed to JavaScript, adding a new context object used when initializing the JavaScript files.
- JavaScript files for widgets are now dynamically loading, instead of being hard-coded in templates. These files are now required to be listed in the widget WTForm definition.
- Removes unused Blueprint code and removes no longer needed containers.py file, moving it's content inside Holding Pen blueprint.
Co-authored-by: Dinos Kousidis <konstantinos.kousidis@cern.ch>
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>