chat - oldest/newest timestamp handling rewrite
this fixes an issue that, in theory, could have occured with the public chat fetching and over 200 sequential skipped ([secure]) messages. the recent change to skip SYSTEM_NARROWCAST for faction chat was much more likely to trigger the same issue
also
- lighten the red colour used in public chat - was almost impossible to read before
- set the faction chat message count to 100 (it was 50, then bumpped to 200 briefly to work around chat issues)