Add separate posting options for CREST links

- Posting kills via CREST link can now be enabled/disabled seperately
- Own password for CREST link posting can be configured
- CREST link posting can also be configured without password
  (Makes sense as the kill is taken from the CCP CREST API)
Make posting CREST links require a password as default
Version bumped to 4.0.7.1

updated README for version 4.0.7.1 and added version history
Added DB updates for inventory flag conversion

Added update scripts for converting legacy item flags in kb3_items_dropped
and kb3_items_destroyed to CCP inventory flags