non-blocking call to Rasa server

[TathagataChakraborti]

Feature description
Currently, gitbot requires launching the Rasa server seperately.

Solution 1: Be able to do something like rasa_nlu but I could not replicate the classification result with the old models.

Solution 2: Make a non-blocking call to the Rasa server in the install script -- not ideal coz this will keep the server up for eternity even if the skill is not active (we can make a kill call in the destruction code for the Agent class though).

Acceptance criteria
The user should not need to manually launch a different script.