URL Upload plugin

[ron4mac]

Here is a port/rewrite of a CPG 1.5 plugin that provides an upload method for files via URI/URL.
Based on original work by Jascha Schubert <Link>

[gmc]

Added support for 'Custom fields for image description' requested by a client.
If defined in Config, the fields are added to the display to provide information at upload time.
If not used, there is no change to the display.