Changed the importing and file opening system.

formatmanager.py is used to manage all the formats in the formats directory. All formats require at least a load or write function. In addition, they may have other attributes:
name -- the full name of the format
importexport -- true if the format is intended for importing/exporting
extensions -- a list of strings of file extensions
export_options -- a dict of export options

Previously, formats had to be added by adding a new file, changing auto.py, __init__.py, and mainmenu.py. Now new formats (just importing for now) can be added just by creating a file in the formats directory that has the preceding attributes.
In addition, file extensions with multiple corresponding formats (for example xml could mean GraphML or XGMML) are now handled by using the index of the selected format in the import file dialog. Previously, this was handled in auto.py and determined which format module to use by its corresponding extension.

Using Open in the mainmenu is still able to open any supported format by switching to all files. The only thing is that extensions with multiple formats may not be handled properly, as the extension is still used rather than the selected format. Still thinking on how to handle this.

Also fixed the revert function. It wasn't working before. Also you cannot revert imported files.