Implement a filter for unwanted user content.

[RealistikDash]

This issue suggests an implementation of a text filter that removes/blocks unwanted content in user text content (such as messages, comments, level descriptions, etc). Currently, user input of this nature is only verified on the surface level (such as length, character-set). This issue proposes analysing its content (such as censoring or blocking disturbing words and/or phrases).

This is meant to prevent undesirable text content from appearing on servers to create a better atmosphere for regular players.