This makes the StateHandler functional. To reduce the
number of server roundtrips when fetching/updating the
state, the entire state is fetched ocne at bot
initialization and cached. All changes are stored in the
cache and only saved externally after handle_message()
has been executed.
Fixes#141.
This adds support to check and raise a BadRequest when either the
configuration of bot couldn't be found or the BotHandler code of bot
couldn't be fetched. There can be cases where flaskbotrc contains config
details of a bot, but the user hasn't added it's handler class code. This
fixes server to handle such cases, by reporting it to user.
This also fixes the response of bot server to make it possible to skip
the response message.
