Avoid triple reload of posts during paging, etc

Post list was loading post 4 times when each page changes.
This was because the ‘remove’ event is fired for each post
in the list as its replace. We’re moving the fetch() call to
PostItemView.deletePost() since that when we actually
wanted this reload.
Pass posts filter params to map view

Map view now grabs filter params from collection and passes them
to the GeoJSON api when loading posts.

- Moved mapView data url handling to MapView.getDataUrl()
- Add PostCollection.getFilterParams() api to grab filter params
- Pass filter params to jquery.ajax data param
Reset posts filters in 'index' controller

Reset the posts filters when user hits index. Stop calling this
controller internally
on workspace views to avoid accidental resets.