APPS: added mailinglist-manager mini app

- Initial commit of perun-apps project with mailing-list manager app.
- Added README.md with some info about apps.

Common files for all miniapps will come later after some cleanup.
APPS: added common files for miniapps

 - Added common resources files for all miniapps
 - Updated Readme.md
Merge pull request #196 from zlamalp/miniapps

APPS: initial version of Perun's mini-apps project