core: Cleanup gerrit and JIRA references. (#57)

* Remove .gitreview and switch to pulling the main asterisk branch
  version from configure.ac instead.

* Replace references to JIRA with GitHub.

* Other minor cleanup found along the way.

Resolves: #39
(cherry picked from commit 5c6d5ea38f)

BUGS

@@ -1,22 +1,22 @@
 Asterisk Bug Tracking Information
 =================================
 
-To learn about and report Asterisk bugs, please visit 
+To learn about and report Asterisk bugs, please visit
 the official Asterisk Bug Tracker at:
 
-	https://issues.asterisk.org/jira
+	https://github.com/asterisk/asterisk/issues/
 
-For more information on using the bug tracker, or to 
+For more information on using the bug tracker, or to
 learn how you can contribute by acting as a bug marshal
 please see:
 
-	http://www.asterisk.org/developers/bug-guidelines
+	https://wiki.asterisk.org/wiki/x/RgAtAQ
 
 If you would like to submit a feature request, please
 resist the temptation to post it to the bug tracker.
 Feature requests should be posted to the asterisk-dev
 mailing list, located at:
 
-	http://lists.digium.com 
+	http://lists.digium.com
 
 Thank you!