Inital OSM map work that was done on live site.
Final edits and tweaks for a while, going to work on OSM and session stuff on openstreetmaps branch.
Merge remote-tracking branch 'origin/openstreetmaps' into barneshut
Actually I'll keep working in this branch for a while.
Damn -a flag.
Fixes to _session_vars, changes to /canvas/gravity and /map.

/canvas/gravity now accepts a URL query for number of particles.

gammalib now has a function for getting URL parameters by name.

Fullscreen when pressing F10 now works properly, and the settings stays saved.

OpenStreetMap settings stay saved as well.