Not compatible with TM3

[sethfitz]

Tasking Manager statistics were previously loaded from http://tasks.hotosm.org/user_data/<id>.json.

When TM3 was launched, this endpoint stopped working, resulting in exceptions propagating up to the point where changesets couldn't be processed (rather than ignoring those stats).

I patched this in 01b9164 and ff65590, but we still need to restore functionality.

[dalekunce]

new route

http://tasks.hotosm.org/api/v1/user/[username]/mapped-projects

[dalekunce]

@mojodna is this wrapped up.