Add BZDB Settings editor

[allejo]

This PR introduces support for seeing and editing BZDB variables on a map.

To Do

• Finish documenting variables over at Document BZDB settings BZFlag-Dev/bzflag.org#42
• Add support for remaining BZDB types (there's only limited integer/float support right now)

Fixes #45

[TheGiraffe3]

How soon do you figure this will be done? It would be nice alone to have BZWorlds have more customization options.
But also, right now if I add them in by hand and then open the world in WebBZEdit, it'll remove the variables that it doesn't recognize.