Remove forward annotation mode

[reckart]

Is your feature request related to a problem? Please describe. The forward annotation mode only works in very specific situations and has pretty ugly code in the detail sidebar to the right. I doubt that it is used much if at all.

Describe the solution you'd like

• [x] Hide the "forward annotation" functionality behind a feature flag (merged for 0.20.0)
• [ ] If nobody is missing the mode after a while, remove it entirely

Describe alternatives you've considered Having an efficient way of annotating by automatically forwarding to the next annotatable unit is in general a good idea, but it should probably be a feature of individual editor plugins (e.g. a pos/lemma-oriented editor offering quick keyboard navigation) than a general feature in the detail sidebar.

Using a the string matching recommender capability of INCEpTION as an alternative is probably as efficient as the forward mode was.