Feature #104: Use user agent also for HTTP

Feature #104: Use user agent also for HTTP

Now we use the same user agent string for SIP and HTTP requests.

At least one user reported that with "Azure Active Directory conditional
access" enabled the user agent string in HTTP request is no longer
ignored. In that case the user has to set the user agent string to a
concatenated version of <LYNC> and <BROWSER> user agent strings, e.g.
(line feeds inserted for readability):

   UCCAPI/16.0.8431.2299 OC/16.0.8431.2299 (Skype for Business)
   Mozilla/5.0 (iPhone; CPU iPhone OS 10_3_2 like Mac OS X)
   AppleWebKit/603.2.4 (KHTML, like Gecko) Mobile/14F89 Safari/603.2.4

i.e. "Skype for Business client" + "Safari on iOS 10.3"