First implementation for verifying reservations

Provide visual way to see which reservations produce
errors or warnings.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Change date format in periods

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Receipt refactoring!

Remove type. Add datetime and pending field.
Sort them based on date/time creation.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>