[#4832] Add more SCM timing instrumentation.
[#4832] Don't assume scm libs are installed
[#4832] Don't assume scm tools are installed
[#4832] instrument the sidebar for each app separately
[#2584] ticket:256 Allow deleting tickets and undo
[#2584] ticket:256
* removed ?deleted=True from deleted tickets url
* improved tests
[#2584] ticket:256 Simplified ticket's visibility condition
[#2584] ticket:260 Ticket deletion improvements

* add "Show deleted" and "Hide deleted" to the Milestone and Custom Search pages.
* save paging parameters in the querystring
* restore  ticket's title
* Related Artifact doesn't show links to deleted tickets
[#2584] ticket:260 refactored paged_search
[#2584] ticket:260 check  permissions in  paged_search and test