Search resources by taxonomy

The taxonomy is the data structure that glues everything together. It is the meta information about the learning architecture. Thus, the taxonomy is used in the question item pool, the document pool, on learning resource level and for competencies. 

Authors must be able to search for learning resources within a certain field to lookup material that has been released by peers or their own material.

This issue is about adding a search field in the authoring environment to search by taxonomy.  The metadata should also be listed in the learning resource table like it does in the question pool.