Cleanup .gitignore (#84)
Cleanup .gitignore (#84)

Most of the entries aren't needed in this project. This commit additionally
added the following entries:

 * config.json: The file is used by openhab-cloud but should be generated
   during the installation from config-development.json or config-production.json
   and should never be commited, as it is changed per-instance
 * .idea: IntelliJ IDEA and other IntelliJ development environment specific things
   only. Doesn't need to be commited.
 * openhab-cloud.iml: Created during startup of openhab-cloud
marziman/openhab-cloud,marziman/openhab-cloud,marziman/openhab-cloud,marziman/openhab-cloud