Fix the events#show page when an event contains lat/lng information.

The map_marker partial is moved to `views/shared` to be shared globally.

This addresses #490.
UserLocationAgent: Receive events and accept POST via WebRequestsController.

Show the POST URL on the details page while at it.

The old user_location_updates URLs still work.

This addresses #490.
Integrate UserLocationUpdatesController into WebRequestsController.
Merge pull request #504 from knu/user_location_agent-issue-490

Update UserLocationAgent