Conversation session cleanup after flexible timeout.

Situation:

- First time user starts a conversation and converses a bit with the bot.

- During that interaction the bot makes some back-end calls, collects functional and technical data from back-end systems and internal session variables get set that are valid for this conversation at this time.

- The user gets tired, annoyed, interupted, ... and simply "leaves" the conversation before reaching the functional end of the conversation and without a "goodbye" type of message.  In this case the bot doesn't know the user left and waits patiently for the user to continue chatting.

- After X days, weeks, ... the user comes back with a totally different (or even the same) situation.  The bot at this point recognises that the user already had a conversation session and the session is restored with all the internal session variables from before.  However, the situation may be different or may have changed completely now making the internal state of the conversation "wrong".

Feature request:

Have a way to specify a functional time-out on a bot which can trigger a diologstate where the session can be cleaned up.

Sub-Feature request:

Have a new "Action" which can be used to "Clear whole session", "Clear conversation", ... more clear options to clear intents, old dialogstates, all custom session variables, ...