* egw.jsonq() now always returns a promise like egw.request(), still supporting old callback syntax
* egw.link_title(_app, _id, _callback, _context, _force_reload) supports boolean values for _callback (to not break existing code)
- false: just a cache lookup (like current call with just 2 parameters), returning null, if no title is cached, or the title
- true: always return a promise, which might already be resolved, if title was cached
- function: also returns a promise and calls the callback
--> calling egw.link_title(_app, _id) without 3rd parameter is deprecated now (gives a console.trace), to be changed in future to always return a promise, unless called with false, to just return a cache-lookup
* Et2SelectAccountReadonly and et2_link_widget is changed to use the new/updated syntax with promises
- get_select_options seems to be nowhere in use, so I did not implement it
- Et2Select* widgets with static options assign them in their constructor (like the r/o ones)
- removed a jQuery.proxy call, which we dont want in new code
