Added a new configuration variable, PHPCI_BUILD_ROOT_DI.

This variable allows to change where the build happens.
It defaults to PHPCI_DIR.'PHPCI/build/'.

Moved build path calculate and build removal into the Build class.

Also remove the build directory when deleting the build.

Close #834

PHPCI/Service/BuildService.php

@@ -112,6 +112,7 @@ class BuildService
      */
     public function deleteBuild(Build $build)
     {
+        $build->removeBuildDirectory();
         return $this->buildStore->delete($build);
     }
 }