Added images to CMS

Added:
* controllers/admin/image.php ~ image controller that allows viewing,
adding, deleting images
* views/admin/image/image_add_v.php ~ the file upload view for images
* views/admin/image/image_index_v.php ~ the index view for images

Changes:
* config/custom/site.php ~ added image directory and thumbnail directory
to site config
* helpers/view_processing_helper.php ~ upgraded vp_buildForm so that it
can handle file upload forms and also added a parameter for passing the
error string returned from the CI file upload class's display_errors
function
* libraries/AdminController.php ~ added images to the admin nav
Added image validation to project edit form

The system now validates the image file specified in the project edit
form, assuring that the image exists in the image dir.