Clear Cache Button on Configuration Layout

Adds a new button to the configuration layout called "pushClearCache"
that will be usable for viewing the state of the cache and also clearing
it.
Caching Direction Definition in Config Module

Moves the caching directory initialization to the config module, so that
it may be more accessible elsewhere in the program (notably, the code
that initializes the configuration screen).

Also, in the future, it might be nice to let the user specify the
directory to use for caching (and in that way, the user could cache to a
network or shared drive if s/he wanted to share the cache among multiple
instances of the program).
"Clear Cache" Button Initialization

Sets the button and its text up upon opening the configuration dialog
box. This includes the disabled/enabled status and also the file count
when there are files in the cache.
"Clear Cache" Button Implementation

Adds support for disabling the button, removing the underlying files,
and updating the button text when the user clicks it.
Merge feature/google-caching.counter-clear

Brings this experimental feature into the main feature/google-caching
branch after its successful implementation.