* Move a-b to PSR-4
* Move c-d to PSR-4
* Move e+g to PSR-4
* Move h-l to PSR-4
* Move m-r to PSR-4
* Move s-u to PSR-4
* Move files/ to PSR-4
* Move remaining tests to PSR-4
* Remove Test\ from old autoloader
* introduces a method in OC_Image which doesn't stretch images when trying to make them fit in a box
* adds the method to all key providers so that they can do their job, as expected by the Preview class
* improves the caching mechanism of Preview in order to reduce I/O and to avoid filling the available disk space
* fixes some long standing issues
* **contains mostly tests**
