Renamed fields in ProcessLink
FlowDao getRecipients and getProviders are now using FlowDescriptor as
input
Implemented getTechnologyInputs & getTechnologyOutputs in ProcessDao
Check for empty set in getDescriptors(Set)
Fixed error in getDescriptors(Set)
Merge remote-tracking branch 'gdtc/master'

Conflicts:
	olca-core/src/main/java/org/openlca/core/database/RootEntityDao.java