Improvements to plugin gruntfile handling
Improvements to plugin gruntfile handling

* Allow YAML plugin files to also work
* Allow gruntfile specification without adding default targets

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