[TASK] Use include with shutup instead of file_exists

This change uses include with shutup operator instead of file_exists
checks for optimized performance.

Change-Id: Ia2ddef625db70d8c985526978b6d83cebbe4d90f
[BUGFIX] Compile original and proxy class into one file

Reduce amount of file inclusions by combining original class
code and proxy class code into the same file as both need to
be loaded anyway.

Change-Id: I4ff462b68683ef60166a642ad3382af63623c062
[WIP][TASK] Remove file_get_contents call in Cache FileBackend

Change-Id: I8181ee30632a1f0513708a418d977d98bea7144d