Make editing existing vocab easier

[LiamSkirrow]

When editing an autogenerated verb conjugation (or anything other vocab class) the current implementation (elif(mode == MODE_EDIT_VERB): in LangTrainer.py) simply involves printing out what was autogenerated and then giving the user space to rewrite the correct conjugation from scratch. It'd be nice if we could somehow print out the current autogenerated version but allow the user to adjust that text in the buffer, so that they don't have to type something from scratch.

[LiamSkirrow]

This issue should focus on a more general approach in making the process of modifying an existing bit of vocab easier. Think about a way of improving the experience than just simply scrolling through a whole bunch of verb conjugations, modifying them one by one.