geo: Fixup image overlays

Fixup 0405d32eafad9b21375681e6668aee64a1d804de
geo: Fixup configurable boundaries

Fixup d6a3c59aea63da6ea6bde0a60d24ca3adb3750c5
geo: Add imposm mapping file
Upgrade OpenLayers (2.12.1 -> 2.13.1)

The most visible changes are:

* Animated zooming
* Enabled kinetic dragging

See release notes [0] for more information.

[0] https://github.com/openlayers/openlayers/blob/master/notes/2.13.md
geo: rename select instance map class
geo: Update OSM attribution link and style

Attribution now links to www.openstreetmap.org/copyright as recommended.
Previously we explicitly linked to the CC-SA license. As we don't do
this anymore, this is now also usable in installations using data from
ODbL licensed OSM material.

In addition, attribution notes are now displayed nicely within the map.

This is related to #93, which additionally proposes to specify
attribution per map layer.
Correct non-void html tags
Better styling of map controls