API for task/context descriptor persistence. UNTESTED.

relates to #117
Merge branch 'master' of github.com:radek-macha/everBeen

Conflicts:
	been-api/src/main/java/cz/cuni/mff/d3s/been/api/BeenApiImpl.java
Merge branch 'master' of github.com:radek-macha/everBeen
Merge branch 'master' of github.com:radek-macha/everBeen