Added imported_from filter

For supporting the graphite importer via API, now we can search for a
previously imported dashboard
Ignore all egg-info dirs
Handle boolean params better
Update graphite importer to use API

- URLs for tessera and graphite default to app.config, but can be
overriden on the command line
Update JSON import/export to use API as well
Merge pull request #288 from urbanairship/issue-267-import-via-api

Issue #267: import via api