Add Additional Bot UAs

[PseudoResonance]

Would it be acceptable to have a more complicated bot user agent detection? FxTwitter uses this regex for example, although it's also missing the user agent I am personally interested in, matrix-media-repo.

The reason is that at times, certain sites have temporarily blocked access based on user agents containing the string bot, so it is sometimes advantageous to have a more discreet UA... I actually ended up switching my url previewer to use the UA curl, as it seemed to get past those bot filters, while still being detected by FxTwitter. I realize this is kind of a ridiculous request though, but I figured I might as well ask. Thanks for the cool project regardless!