Add pkg appliance

## Feature overview:

+ Separate `gone` into own executable
+ Add concept of 'appliance'
+ Add much more versatile config files by support arbitrary sub-catalogs (roles, hosts, ...)
+ Make modules (actually an appliance) or an isolated folder containing files to be synced

**Note:** In last commit i changed from lowercase globals to uppercase. This is a bit chaotic: catalogs dirname (e.g. `./modules/`) is lowercase, the reference in `$CATALOGS` is lowercase but the variable `$MODULES` is uppercase. Not so sure I like this. 

Let's see what breaks :)