Improve logging and notifications of update check results

When checking for updates on program start, also log the results to the
status messages to make the result more visible to the user.
While at it, changed the wording of a few messages and made the
version check URL a constant.
Set a timeout of ten seconds instead of waiting for the default timeout

Ten seconds should be enough for this simple request. The default timeout
is OS-depent and might be much higher so better set a reasonable
value.
Merge pull request #166 from eht16/updatechecker-improvements

Updatechecker improvements - more notifications and setting a timeout