REL-2064: check for mac networking issue on startup

Provides a warning and stops the application if we detect the Mac / JDK 1.7 [networking issue](http://bugs.java.com/bugdatabase/view_bug.do?bug_id=7180557|networking issue).  I separated out the warning popup handling into a separate `FatalMessage` class that supports html messages with links.  The idea is to refer the user to a support page, though at present I'm not sure if this is the correct URL to use.

Here is an example of the popup.  I think we'll all agree, it is stunningly beautiful.  Suggestions to improve the wording are welcome.  I expect Andy will want to make changes.

![networkingissue](https://cloud.githubusercontent.com/assets/4906023/4811847/1f32b826-5ebd-11e4-896c-1b2439086d8a.png)
In general we should be using the `Platform` class in the core bundle for these kind of OS checks.  I didn't here though because the `edu.gemini.osgi.main` bundle shouldn't depend on any other bundle.