add support for advanced goals, the first one being fibers

[Dieterbe]

this needs wger-project/wger#1664
TODO: (note: i don't plan to work on these, maybe @rolandgeider can do it :-) )

• make the state changing on the plan edit/create form work (changing the dropdown should update which form entries are shown)
• update goals and logs widgets.

[coveralls]

coverage: 67.442% (-0.08%) from 67.522%
when pulling 9e87168 on advanced-goals
into 73174d7 on master.