Change Summary

This PR adds a new mod type called Action Mods, which are triggered by post content. It includes a tipping mod which is of this new type.

Further ideas:

• onSetInput and onAddEmbed callbacks should apply to the reply of the post being called on
• onSetPostContent - a callback for modifying post content (this can be done by adding a section for modifications by the Mod)

Merge Checklist

• PR has a changeset
• PR includes documentation if necessary
• PR updates the rich-embed examples if necessary
• includes a parallel PR for Mod-starter and the gateway if necessary