modification date inserted at client to improve performance
Merge branch 'development' of github.com:opentox/opentox-client into development

Conflicts:
	lib/compound.rb
Merge branch 'development' of github.com:opentox/opentox-client into development
rdf serialisation of modified objects fixed. DC.modified removed.
Merge branch 'development' of github.com:opentox/opentox-client into development
Merge branch 'development' of github.com:opentox/opentox-client into development
openbabel requirement removed. initial descriptor classes.
Merge branch 'development' of github.com:opentox/opentox-client into development

Conflicts:
	lib/opentox.rb