BpkStore - removed exception signature from task context / task context descriptor listing methods (these exceptions are never thrown), fixed documentation for both methods
Merge remote-tracking branch 'origin/master'

Conflicts:
	software-repository-fsbasedstore/src/main/java/cz/cuni/mff/d3s/been/swrepository/FSBasedStore.java
	software-repository-store/src/main/java/cz/cuni/mff/d3s/been/datastore/BpkStore.java
Fixed TD and TCD xsds
  * 'mainClass' subelement in 'java' element marked as required
  * minimum required count of 'task' subelements in TCD changed from 0 to 1.