Rework Location Mapping

[vauvenal5]

In future we want to be able to set more then one location mapping, allowing for a more fine grained definition of storage locations.

Some additional thoughts:

• When implementing this we should also consider the cache as a viable storage location for downloaded files. #82
• We should also consider the ability for a read only-mapping. This would allow to point to existing images from the NC Files app without saving new once to that same location.
• Also checkout the NC Files app behavior of not properly recognizing files which where downloaded by Yaga.

[vauvenal5]

Also consider how clearing the cache folder regularly could be solved automatically.