First try at implementing tags. Maybe not the best approach but it works!
Reimplemented tags using only one class (Tag). Dropped TagName.
Implemented Tags the right way.

	- Tag creation;
	- Tag association with messages;
	- Tag disassociation with messages;
	- Tag deletion;
	- Tag retrieval by name;
	- Tags retrieval by message.
Successfully merged with master. All green.

Merge branch 'master' into tags

Conflicts:
	iris-core/iris-test.db
First working implementation of Tags with Lucene!
Finished implementing TagDAO for Lucene.
Merge branch 'master' into tags

Conflicts:
	iris-core/iris-test.db
	iris-core/src/main/java/br/unb/cic/iris/core/model/Tag.java
Finished implementing Tag functionality.