Clean up configuration cruft (editor specific, and unused files)

[Enrico2]

I looked into the various configuration files we currently have checked in, after reading the issue (#86) that was opened on whether or we should have any editor specific files in the repository.

I noticed we check in some files that are not used by anyone, a file that is likely only used by me (and only rarely tbh), and some that we can move to to a designated folder, to reduce some of the clutter without affecting editor functionality.

This PR brings the repo to a state where the only editor specific files are contained in .idea. As we discuss the issue mentioned above, we might end up removing this folder all together, but I'd like us to make that decision against this PRs version of the repository (cleaner, less cluttered, reflects one of the suggestions in the issue)

Commits:

• Move all IntelliJ config files to .idea
• Delete cli/.graphqlconfig -- this doesn't need to be checked in to make anyone more productive in a significant or commonly used way (i.e. this is only for IJ users with a specific plugin and can easily be created locally. I've added it to .gitignore).
• Delete config files that we don't use (.travis.yml, bulk.yaml, vagga.yaml) that were copied over when we forked graphql-parser.
• Rename the github.gql file to use the more common, seemingly agreed upon, file extension (.graphql, see Recommend an extension to use graphql/graphql-spec#203 (comment)).

[ashleygwilliams]

i'm still not convinced we should have these files in this repo, but this is certainly a big improvement! thanks for doing this!