Use a non-cache folder for keeping the cache

[merlos]

Open GPX tacker Cache is a key feature of the application to support offline.

Currently the cache is kept in a folder that the iOS can clear automatically without the user consent. This is because cache folders are supposed to be used for storing non critical data.

Given that the use has the option to delete the cache at any time if needs space and the criticality of the cache for offline, it makes sense to move it to a regular folder.

This should be added as an option in MapCache, so in the config it can be chosen to keep the cache in a cache folder or in a regular app data folder. Set it up in GPX tracker to use data.

Related with #229