Have sidebar push the map on reveal

This avoids cuts of visible parts of the map and helps to
implement better GtkPopover positioning over the map view.

https://bugzilla.gnome.org/show_bug.cgi?id=722871
Add MapMarker and MapBubble classes

Add base classes intended to create markers associated with
content rich GtkPopover based bubbles.

https://bugzilla.gnome.org/show_bug.cgi?id=722871
Add UserLocationMarker

The user location marker is now based on MapMarker class,
supporting MapBubble to show a GtkPopover based UI for the
user location information. This removes UserLocation which is
based on MapLocation.

https://bugzilla.gnome.org/show_bug.cgi?id=722871
Add SearchResultMarker

The search result marker now is based on the MapMarker and
MapBubble classes. This improves the UI and the information for
searched places.

Adding complete support for most Geocode place types is a
pending task.

This also removes MapLocation class.

https://bugzilla.gnome.org/show_bug.cgi?id=722871