Global cache for GIS requests

[martinhecher]

Implement a global cache used among VMANIP modules. The ideal implementation would be a 'transparent bridge' system, where a module simply does an ajax request, without explicitly querying the cache. Via the 'transparent bridge' the request is checked automatically and a cache hit is returned, if available.

Inspiration can be found at:

http://stackoverflow.com/questions/6899855/how-to-create-custom-cache-mechanism-for-ajax-calls-using-localstorage-in-jquery