ADDED: Base class for managed network resources (Circuits & Bandwidth)
UPDATED: Constants class

CHANGES:
- NetworkResource contains all the common details for Circuits and Bandwidth
- Removed PHEDEX naming references (PHEDEX_FROM_NODE => NODE_A)
- Added the concept of a uni/bidirectional resource
This might come in handy when we move the central level and we want that
for a resource reserved between A and B, that only A->B uses it.
UPDATED: Circuit now uses the NetworkResource base class
- lost of additional updates as well as naming changes
ADDED: Tests for the NetworkResource base class
UPDATED: Tests for the Circuit class

All related tests now reside /NetworkResource/Test...
RENAMED: CircuitManager->ResourceManager
UPDATED: ResourceManager to make use of new Circuit class
UPDATED: All tests for CircuitManager
UPDATED: All other class that used or were used by CircuitManager and Circuit
ADDED: Class for managed bandwith (WIP)