NOTE: these changes may break code!!
I've reworked the show/hide button methods to clearly separate
requirements of derived class from the base class.
The base class needs to show/hide buttons depending on the state of the
UI (e.g. in/out of edit mode).
Derived classes however need to disallow certain buttons regardless of
the state the ui is in and these disallowed buttons need to be
remembered.
Merge branch 'master' of https://github.com/rlsutton1/VaadinUtils.git
fixed a possible bug where the entity manager was only being reset when
an exception occured.