Add local analytics

[zafarali]

• Message Counts
• User engagement
• Common Questions
• Failed answers
• Anonymized (?)

[adelzaitri]

@zafarali Do you still need help here?

[zafarali]

Hey! it would be great if you could make a small initial contribution!

Some clarifications:

1. By "local" solutions I meant that it doesn't work to bot analytics platforms. It's more for you to download and analyze layer.
2. Ideally the solution should be lightweight (json read/write files or a very small self-hosted database that is compatible with heroku or openshift)