Improving the docs of the RequisitionsService
Adding helper functions on RequisitionsService for managing foreignSource definitions.

The service currently have implementatd the following functions using
local data:

getAvailableDetectors()
getAvailablePolicies()
getAvailableServices()
getAvailableAssets()
getAvailableCategories()
getPolicyKeys(policyClass)
getPolicyActions(policyClass)
getPolicyMatchBehaviors(policyClass)
getPolicyParameters(policyClass)

Pending Implementations:

getDetectorParameters(detectorClass)

The AssetController has been updated to use the RequisitionsService to
obtain the list of available assets.

The DetectorController has been updated to use the RequisitionsService
to obtain the list of available detectors.