Fix gitignore for plugin filtering
Fix gitignore for plugin filtering

The previous incarnation was overly heavy-handed such that new
files in packaged plugins did not show up in `git status`. This
version now makes all files in known plugins show correctly, and
still hides all untracked plugins.

chrismattmann/girder,kotfic/girder,Xarthisius/girder,Xarthisius/girder,msmolens/girder,salamb/girder,opadron/girder,data-exp-lab/girder,msmolens/girder,manthey/girder,msmolens/girder,sutartmelson/girder,Kitware/girder,adsorensen/girder,data-exp-lab/girder,jcfr/girder,girder/girder,manthey/girder,opadron/girder,salamb/girder,adsorensen/girder,manthey/girder,RafaelPalomar/girder,salamb/girder,chrismattmann/girder,kotfic/girder,sutartmelson/girder,manthey/girder,salamb/girder,kotfic/girder,kotfic/girder,sutartmelson/girder,essamjoubori/girder,chrismattmann/girder,jcfr/girder,chrismattmann/girder,RafaelPalomar/girder,adsorensen/girder,essamjoubori/girder,girder/girder,opadron/girder,data-exp-lab/girder,essamjoubori/girder,data-exp-lab/girder,jcfr/girder,adsorensen/girder,girder/girder,jcfr/girder,jcfr/girder,jbeezley/girder,RafaelPalomar/girder,Kitware/girder,Xarthisius/girder,salamb/girder,Xarthisius/girder,Xarthisius/girder,jbeezley/girder,sutartmelson/girder,jbeezley/girder,essamjoubori/girder,chrismattmann/girder,essamjoubori/girder,girder/girder,kotfic/girder,RafaelPalomar/girder,data-exp-lab/girder,Kitware/girder,RafaelPalomar/girder,jbeezley/girder,opadron/girder,Kitware/girder,sutartmelson/girder,msmolens/girder,msmolens/girder,adsorensen/girder,opadron/girder