Replace Kalendar with Merkuro in mappings

This commit replaces the mapping for Kalendar to Merkuro due to Kalendar being renamed to Merkuro and that bugs no longer go to the new product on Bugzilla with DrKonqi

Also, should an entry for kalendar be added to mappings as well? The only reference to Kalendar I could find was kalendarac (which this commit updates), however the bug report I looked at said the binary was kalendar and was sent to the kde product despite this working in the past before the product rename.