GUI elements

Added GUI elements diagram. Not done anything to it yet.
GUI elements + check in/out diagram

Added some more to gui uml diagrams.
Updated gui diagrams

Updates gui diagrams:
- PunchCardModel now implements observer interface
- PunchCardDropDown now implements notifier interface.
- Sequence diagram for check in/out done.
Merge remote-tracking branch 'origin/master' into gui
New punch card diagram

Added aa sequence diagram for inserting new punch cards.
Current selection diagram

Added a sequence diagram showing how to update currently selected punch
card.
Analyzer diagram

Added a dequence diagram detailing how to analyze a punch card.
Merge remote-tracking branch 'origin/master' into gui
PunchCardObserver

Added the PunchCard observer interface, stating the responsibilities of
an observer. Used by the GUI.
Notifier

Added the Notifier interface, stating the responsibilities of a
notifier. Used by the GUI.
PunchCardModel

Added the PunchCardModel interface, stating the added responsibilities
of a model. Used by the GUI.
PunchCardModel JavaDoc.

Added JavaDoc to PunchCardModel.
PunchCardModelImpl

Added PunchCardModelImpl. No implemenatation yet, as well as no tests.
Should probably be merged with master now...
Merge remote-tracking branch 'origin/gui'