Conversation improvements: help and reset

[ehrhart]

This is an attempt to discuss about the ways to improve the guidance and conversationality of the bot.

Help

As noted before, the bot lacks a basic set of help messages.
For example, when the user says:

how
help
what can you do
???

Expected result:
The bot should display a list of questions that can be asked.

Reset

At any point in the conversation, the user should be able to cancel the action by saying:

nevermind
nvm
bye
cya
let's start again

Expected result:
The bot should cancel the follow-ups and forget about the current conversation.

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Feedbacks and suggestions are welcome!

[rtroncy]

+1 This amounts to add more training sentences and default intents. This should be added on the 2 DF projects: light and full