created package

moved relevant files
created bundle
edited bundle
added add task method
created methods

display and print task
printTask

tentative method
tentative display method
renamed var

commandStack renamed to undoStack
undo and redo

undo partially done
Merge branch 'master' into database
Group relevant classes into database package

Why is this change necessary?
For better organisation of database-associated classes.

What side effects does this change have?
- Developers wanting to use classes under the taskbuddy.database package
  have to now import the latter.
- All classes in taskbuddy.database have to be public, otherwise other
  developers in the same project cannot use the database classes.