Add overmap special json

	new file:   overmap_specials.json
Selecting/verifying overmap special placement locations
First test (crashes)
Successful test run
Car stereos
Added stereos to item groups
Stereos need a cd to play
Fixed the wrong Id in item groups
Stereo saves
Fixed melee.json spacing getting messed up
better sounds for the sterep
Update flags/connections/placement code
Show Message every 5 turns
Merge remote-tracking branch 'origin/master' into stereo
Item_factory: add support for loading items of type it_stationary.

- Simplify the constructor of it_stationary to make it usable in Item_factory (all the values of it_type are loaded _after_ the object has been created).
Export the flyer item to json.
Allow snippet texts to be read from an array

instead of having each entry in a separate json object.
Add documentation for json type STATIONARY and snippet.
Add extraction of translations for stationary items
Submap refactor: Add accessors for submap::graf