Improve the speed of the ReST API and Service Layer for the requisitions' repositories.

The current WebUI for requisitions works fine for a few requisitions, and a few nodes per requisition.

On those environments with hundreds or thousands of nodes/requisitions, the WebUI is unusable and it takes several minutes to render on each change. For these situations, it is better to use the ReST API directly or provision.pl. Unfortunately, the ReST API is still slow when dealing with big requisitions and/or thousands of requisitions.

There are several strategies for the requisitions' repository management that are not being used. There is one of them designed to maintain a cache in memory that makes the response time almost immediately (FasterFilesystemForeignSourceRepository). This class was using a custom implementation for a Directory Watcher, that works but not for all cases. This class must be redesigned to use the Java7's libraries for file changes watcher.

Also it would be good to be able to select which strategy must be used by Provisiond and the ReST API.