Replace operation links in the widget with a dropbutton

This would be a wonderful addition and in my eyes definitely needed for a better UX.
But unfortunately this is not applying anymore on the latest dev version.

To prepare for this, the sorting of links is changed in above patch, since '#type' operations does not seem to support the weights.

Please find a reroll against current code base. I have re-arranged the code base, to the patch only contains the intended changes.
Please check if the patch is correct.

I have some remarks:
- from UX perspective, it is undesirable that an extra click is needed to see all available options.
- not sure what 'close the dropbutton'. also, 2 calls are done against different classes 'open' vs. 'dropbutton-open'.
- when the first operation is hidden, an empty operation is added. this is not so in the original code. perhaps the class 'open' can be set always?
- operation 'add time slot' works fine, but is initially not set ok.(must only be shown if no next slot exist)
- operation 'clear/remove' does not work. I cannot find why
- operation 'copy previous day' works fine.

Above commit fixes the problem with operation 'clear/remove'.

This reroll fixes the lost functionality of sorting the operations, according to the 'weight' attribute (Note: not '#weight').
It still contains the 'bind's to the old links. They must be removed, eventually.

Above patch makes sure each link is on its own line.
Much like permanently expanded dropbutton.

For further work, see also #3476793-15: Fix accessibility issues in form → , that also changes the links to buttons, taking another approach.

For context, using links (especially empty links) are setting up barriers. Since all action links are in fact triggers for functions, we provided a patch (see related issue) replacing them with submit buttons and providing audible feedback.

The approach to bundle the action links in a dropbutton was so appealing that we transformed that into a button-based dropbutton (see Paragraphs for reference).

Well aware now having two different further development approaches in two different issues. Hope we can merge that somehow.