Change security-proxy so that sec-username and sec-roles always are removed.

Added new header provider in security-proxy that checks the currently logged in user and if that user is one of the "special"/"trusted" users then it will map

imp-username -> sec-username
imp-roles -> sec-roles

Allowing trusted users to impersonate another user.  This is required for the extractorapp to enforce the security on the end user.
Add test for ExtractorLayerRequest class
add wfs extractorapp test
Merge branch 'AddExtractorappTests' into extractorapp-improving-automated-testsuite

Conflicts:
	config/defaults/security-proxy/maven.filter
	extractorapp/pom.xml
Test KML extraction.
Adding utests on GDALCommandLine

TODO: not sure on what to test actually, it might be improved, need to
see with @jeichar.