adding metadata and bookmarks models

app/models/_orientdb_models/attribute.rb

app/models/_orientdb_models/bookmarks.rb

app/models/bookmark.rb

app/models/collections/context.rb

app/models/collections/institutions_context.rb

app/models/collections/public_context.rb

app/models/collections/user_context.rb

app/models/collections/user_private_context.rb

app/models/collections/user_public_context.rb

app/models/concerns/orient_db_serializable.rb

app/models/learning_object.rb

app/models/metadatum.rb

app/models/user.rb

app/models/validators/collection_owner_validator.rb

db/migrate/20160125131441_create_metadata.rb

db/migrate/20160125132447_create_bookmarks.rb

test/fixtures/bookmarks.yml

test/fixtures/metadata.yml

test/models/bookmark_test.rb

test/models/metadatum_test.rb