Change what Timetable shows depending on DataProvider and View selection

If no DataProvider is set, it shows only a "not available" message.
If no Entity is selected, it shows the DataProvider's empty Timetable.
Dataprovider's empty timetable is shown when a Subject is selected
Add GetCellInfoVisitor in TimeTableModel

Timetable shows different informations based on what type of Entity is
selected
Add dataprovider for relational databases
Add linux, win32 specific fragments to the feature
Add empty wizard functionality for database
Add schema generation to dataprovider extension
New wizard persists an institute in the db

Entities implement Serializable
Indroducing AbstractEntityDb as a MappedSuperclass
Add "Open database" wizard
Add Save As feature

Database implements Save As feauture
Add hibernate dependency

Update pom.xml with elver repository
Add main menu contribution in dataprovider.db extension
Add JaCoCo and Coveralls integration
Integrate Travis CI with Coveralls
Add Preferences menuitem

With Database preferences page
Change actions to commands

Change NewWizard, OpenWizard, SaveAs actions to commands.
Remove test actions from core.
Add RefreshCommand to dummy.
Add dialog for creating assignments
Add Connection extension
Add ConnectionPreferencePage functions

Can add new connection from the Connection extension point.
Can save & load connections with the PreferenceStore
Add plugin org.confetti.dataprovider.db.mysql

This plugin implements the Connection extension point