#37 Fixing notice delete form

This MR fixes the current delete-form problems: + Showing in tombstones + Being broken due to the changes on URLMapper and the ActivityVerb plugin overwriting the deletenotice path The [previous work]( https://notabug.org/diogo/gnu-social/pulls/34) in ActivityModeration was reverted since 1. this MR provides a simpler and more elegant solution to above problems and 2. I wasn't sure if ActivityModeration was originally introduced to fully control the delete verb.