Add ability to display pin(s) on the map

[benoit74]

See what has been removed in #58

According to @kelson42 (correct me if I'm wrong), the bare minimum to have this in a ZIM is to be able to:

• display the pin on the map
• user can move the pin (needs to support mouse + touchscreen)
• user can copy resulting coordinates in his clipboard (including on touchscreen)
• coordinates should be displayed next to the pin
• this list probably needs to be refined further (especially what users can do with that, e.g. is "copy to clipboard" sufficient)