Separate compilation to an assembly of the OSVR Unity source #38

What it says - don't ship the whole OSVR-Unity source in the binary .unitypackage but rather build and ship a compiled assembly. A few reasons:

• User changes in that code at an individual project level are not recommended - if you want to contribute, the source is the way - because in case of updating to a new version, those changes would get overwritten.
• Would allow us to replace the assembly in already compiled Unity applications (I think?) to fix bugs, etc, just as we can do with the rest of ClientKit native and its deps.