GTNPORTAL-3506 Allow multiple apps registering the very same AMD paths

`newPrefixesToTargetPaths` on line 148 is right. On line 150, we check if it is the case 2 or case 3 as described  the method JavaDoc. Case 2 (same target paths add as available) is acceptable and we only need to store the info from which context path is the request coming (so that we can remove it on context undeploy later in the future). 3 is not acceptable and we throw an exception.

There are also test cases for the two cases:
* This is for case 2: https://github.com/ppalaga/gatein-portal/commit/a81ff30fdf8ee5423d8b44c2729de4f7906f067d#diff-8dd9a38cb9e0291a4708263deaacfcc0R138
* and this is for case 3: https://github.com/ppalaga/gatein-portal/commit/a81ff30fdf8ee5423d8b44c2729de4f7906f067d#diff-8dd9a38cb9e0291a4708263deaacfcc0R125