Let WordSelector class manage the current mode and minimun num of letters

This change is made so that an instance of WordSelector can be passed to the
MenuBar class and have the mode changed within it, instead of passing the
whole (reference of) TypePanel class.
Pass WordSelector instance to MenuBar class

This change is made so that MenuBar can change the mode directly.
Implement changing modes
Merge branch 'modes' into menu

Changing modes feature is implemented.