Feature: Full support of unstable network connection and better handling of issues with Stapler.

Build Monitor:
* no longer displays an error dialog when a connection error happens, but instead tries to re-connect and notifies the user about progress in a much more subtle way
* can handle internal Jenkins errors such NullPointerException incorrectly returned by Stapler as "200 OK" responses (more details can be found at https://issues.jenkins-ci.org/browse/JENKINS-21132)

Resolves #33 and closes #36