[WIP] Added go get inspection support (fixes #336)

This adds ``` go get ``` support via inspections.
I'm not sure it's the best way to do it but it's better then nothing I guess.

There's only one thing that I don't know how to fix right now: after running ``` go get ``` I need to refresh the folder so that the contents gets parsed again. I'll try to ask JetBrains guys tomorrow if there's no answer by then.

Thanks.