Add option to hide channel operation (traffic) messages (join, part, mode, etc.)

[MagnusOxlund]

It's currently not possible to exclude channel operation messages, specifically traffic messages, e.g., "user has joined", from channel flows. In heavily populated channels with little activity or during quiet periods, the many traffic messages make it difficult to find and to follow dialog:

Limechat already allows filtering out messages based on keywords, but using this feature to filter out operation messages risks filtering out actual dialog that also matches the keywords used.

Traffic messages are already separated from regular communication with a green font, so it seems natural to allow the user to safely exclude it completely.

[MagnusOxlund]

I'm closing the issue. The option is found under "log".