Added circular JSON handling to forwardToMain

[tonyanziano]

When connecting to a Direct Line Speech enabled bot, the Web Chat speech adapter object embedded in one of the redux payloads contained a circular JSON structure -- privReco property -- that was causing the JSON.stringify() call in forwardToMain.ts to fail.

This was ultimately causing the Redux action to fail, which resulted in an undefined speech adapter object being sent to Web Chat. Web Chat could not complete the connection to the DL Speech channel.

---

This PR adds error handling for this specific case, and will bypass forwarding the speech adapters update action over to the main process of the app. It is not needed in the main process's state store anyways.

All other errors will be thrown like normal.

As an example, here's what the error message looked like:

Converting circular structure to JSON
    --> starting at object with constructor 'p'
    |     property 'privReco' -> object with constructor 'D'
    --- property 'privRecognizer' closes the circle"

[coveralls]

Coverage decreased (-0.02%) to 67.823% when pulling 6a89d4a on toanzian/speech into 860b5f2 on main.

[corinagum]

LGTM - just one question