more tests are added
tests with events are added for BuilderTagBase/EventTag
the re-usable classes are moved to separate .java files
1) more tests are added;
2) the EventTag tag could now be an indirect descendant of the BuilderTagBase tag to be registered as an event handler
PushEventsJspFragment is renamed to CallTagsJspFragment
1) event name presence is checked explicitly by BuilderTagBase;
2) exception messages are formatter as sentences;
3) more tests are added