Email and IRC build notifications

Always send build notifications to pywikibot-commits@lists.wikimedia.org
as even successes may have slightly different output, and the build
email signals that the build is completed.

Only notify IRC on changes, and reduce the IRC build notice to one
message which will wrap onto two lines.

Change-Id: I5cc6e11e6bf5ecb2da83f9b1c4d5c40ea9caa694
Merge "Email and IRC build notifications"