entitry is only viewable when the classes are shown

should fix #744
Installation of postgresql-9.3 documented.
Merge pull request #754 from ontohub/744-show_only_entity_tree_when_it_should

entitytree is only viewable when the classes are shown
fix ontology spec: file deletion
fix onto deletion spec and implementation
Merge pull request #762 from ontohub/755-brittle_spec

755 brittle spec
Merge branch 'staging' into 739-parse_mappings_correctly