Rename PoCService to PoCRequestService

Change made to follow the name of the superclass RequestService the same
way as PoCRequestManager extends from RequestManager
Add a new sample to test the different Request types (GET, POST, ...)
UI improvement in HomeActivity
Prevent GET and DELETE url from having an empty ? if there is no param

In the case of a GET or DELETE call without any parameter, the constructed
URL was "http://mywebsite.com/mypage?"
This CL removes the useless ? at the end in this case.

Fixes #27
Fix some issues with RequestTypesActivity