now the lern-interval is calculated by the last exam (- 2 month)
now the algorithm checks if a user has marked a date as "home"
merge
improved the algorithm, that calculates the lernplan
- after the klausur, the fach is not learned anymore

Merge branch 'master' into plan_algorithmus

Conflicts:
	server/src/de/duelp/backend/MySQLAccess.java
	server/src/de/duelp/backend/Planer.java