Add ability to filter specific sources

[Cphrampus]

As mentioned in #413, it would be useful to be able to filter out specific sources, such as Ravnica or Eberron, that do not fit the campaign world/are not desired.

The main/initial problem I see is the addition of new sources and the need to maintain a list that could be checked via argparse, but that still may be best so the user is aware of the sources available.

[Trokkin]

Possibly create an xml file listing the sources, then the script can automatically detect what objects are from which sources and remove whatever is passed to arguments
I might experiment with this when I'll have some free time