added a new db column (visits) which acts as a counter for visits per token by users
Sends token & comment when the chat session starts

Sends token and comment of the related ticket to the support assistant
at the start of the chat session without sending them to the user's web
UI.
using .text() instead of .html() to prevent xss attacks
Swapped variables for constants in prodromus.js
using django's slice instead of truncatechars
using <a> instead of <span> for links
Using @staticmethod instead of instantiating Token() objects
removed Token.get_token()
[#12625] Stops prodromus from eating http/https links

The webchat UI previously ate http/https from links as a form of
simplifying/beautifying urls but that proved bad when users copy/pasted
logs so now it displays full links instead of simpler ones.
[#12626] Fixes multi-line support in webchat
Merge remote-tracking branch 'sherief/webchat_patches'