core: Cleanup gerrit and JIRA references. (#40)

* 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

contrib/scripts/ast_grab_core

@@ -67,4 +67,4 @@ echo Notifying admins of the core.
 echo Done.
 echo
 echo Reproducible deadlocks should be posted with a full backtrace and instructions
-echo to reproduce the issue at https://issues.asterisk.org/    Thanks!
+echo to reproduce the issue at https://github.com/asterisk/asterisk/issues/    Thanks!

contrib/scripts/sip_to_pjsip/sip_to_pjsip.py

@@ -1321,7 +1321,7 @@ if __name__ == "__main__":
     # configuration parser for sip.conf
     sip = astconfigparser.MultiOrderedConfigParser()
     info('Please, report any issue at:')
-    info('    https://issues.asterisk.org/')
+    info('    https://github.com/asterisk/asterisk/issues/')
     info('Reading ' + sip_filename)
     sip.read(sip_filename)
     info('Converting to PJSIP...')

contrib/scripts/sip_to_pjsip/sip_to_pjsql.py

@@ -70,7 +70,7 @@ if __name__ == "__main__":
     sip_to_pjsip.sip = sip
     sip.connect(user,password,host,port,database)
     print('Please, report any issue at:')
-    print('    https://issues.asterisk.org/')
+    print('    https://github.com/asterisk/asterisk/issues/')
     print('Reading ' + sip_filename)
     sip.read(sip_filename)
     print('Converting to PJSIP realtime sql...')