JBIDE-18678 Make dependencies to org.jboss.tools.usage optional

@kmarmaliykov I didn't realize this check is so critical.

Regarding the proposed options.
1. This is the easy way to go now, but I don't like duplicating code. In my experience it proofed to be error-prone when update in this code is necessary.
2. I suspect that the LinuxSystem class landed by chance in the org.jboss.tools.usage bundle, because I don't find any relation to the usage reporting. So, it deserves to be in a separate bundle. The problem is that this is a breaking change - all code that depends on this class needs to be refactored.

Which leads to a third option. Copy the LinuxSystem class in a new bundle and deprecate the existing one. In addition, the existing one can be refactored to be a proxy of the new one without changing its API.

Let me know which direction should I take.