Restrict bot actions to channel types

[lakhoune]

1. Motivation - Sometimes a bot might need to restrict certain actions to only be available in private chat or vice versa.
2. Specification - The bot creator should be able to specify if a bot action should only be applicable in private channels.
3. Finalised state - On the canvas, when selecting the bot action element, the properties page displays a select menu. The bot creator can select the types of channel for which that bot action is allowed. He can choose between private, public, 1on1 conversation or all types. Per default all bot actions allow all types.