Possible to exit edit mode while specifying a new feature

[Matthias Schoettle]

When the "edit done" button is pressed while the user is creating/specifying the new attribute or operation, edit mode is disabled and the keyboard stays opened (which still allows to specify a new feature).

Instead, this should be prevented until either the new feature is created or cancelled.

[Matthias Schoettle]

Fixed issue #51: Edit done button wasn't disabled/enabled when all other buttons where disabled/enabled (in disableEditButtons()/enableEditButtons()).

→ <<cset dd9dd2b9cf2a>>