Various bug fixes + local files support.

I noticed a few issues while using the plugin, mostly with the "-p" trigger to make maps permanent and it all went downhill from there.

This fork supports local files as well as URLs, the former are (theoretically) restricted to the {ImgMapDir}/maps/ directory. We tell one type from the other because in this context the URLs should probably start with "http://".

I also added a /maps command that lists the contents of the before mentioned maps directory, in practice those should be bmps, jpgs, etc.