adding editorconfig

tells vim & others the proper golang formatting
move configuration settings into a file

Added new config.go with a ConfigFile type to access the various
configuration details.

The `localPath` and `dropboxPath` have been moved into this configuration as
well.

By default the file should exist at `$HOME/.icebridge` and should be a
json formated file.

```json
{
  "client_id": "APP_CLIENT_ID",
  "client_secret": "APP_CLIENT_SECRET",
  "token": "YOUR OAUTH TOKEN",
  "local_path": "FULL PATH TO ARCHIVE FILES LOCALLY",
  "dropbox_path": "PATH ON DROPBOX TO ARCHIVE"
}
```