Move caching to a system service

[conaticus]

There is a caveat to the current caching system.

Firstly, the cache will only stay up to date if it is constantly watching the filesystem. Right now the cache can only watch the file system if the file explorer window is open. As well as this, when booting the operating system and powering off there is a good chance some file changes will be missed between the program opening/closing and the system turning on/off.

These factors need to be taken into account when implementing this enhancement.