[DONE - REVIEW] Signs

Game flavor. Good for marking dangerous areas (mine fields, see issue #7800) or other things.

- [X] Sign construction and furniture def.
    - [x] If sign is bashed or deconstructed, delete any cosmetic signage stored in the map square (signs can't do it themselves, they don't they have writing on them).
- [x] Writing on sign (added a map<string, string> cosmetics collection to submaps. Maybe I should just have signs be like graffiti and be a single member...).
- [x] examine function for signs (reading and writing new text on a sign).
- [x] sign writing shows up in info when cursor is over the sign.
- [x] sign writing shows up when walking over sign.
- [x] signs plus writing defined for mapgen.

Open to suggestions, the above are what I'd like to put in.
I really need to get the same warning level that you have, which I thought the basic build targets did. Which make target do you use for the builds? The presence or lack of the (void)p doesn't throw any warnings or errors in my build, which is:

    make NATIVE=osx OSX_MIN=10.7 RELEASE=1 TILES=1 LOCALIZE=0 CLANG=1