Remove dependency on UI from usage plugin.
    - Move getApplicationId() from PingStartup to UsagePlugin
    - Move PingStartup to UI plugin and have it just call UsagePlugin.getDefault() to force loading of the usage plugin
    - Remove dependency on eclipse UI plugin from usage plugin now that IStartup was moved to our UI plugin.
    - Move PingStartup's old code into a new SendPingJob that is internal to usage plugin and gets scheduled on plugin start (and cleaned up on plugin stop).
    - Move some clsses to internal package.
    - Don't export internal package (so move some classes to external package).