v0.8.12, build 174

Added an e-mail writing assistant.
Added the possibility to preselect some e-mail writing assistant options.
Improved chat page by scrolling to the bottom after loading (configurable; default is on).
Improved all assistants to provide a button to copy their respective result to the clipboard.
Improved the content validation for the agenda assistant.
Improved the language handling of the agenda assistant.
Refactored the "send to" implementation of assistants.