Added option to disable Soomla Unity based messages

The Soomla Unity code produces quite a bit of messages in the log (both in Editor and when running native). This is fine when setting up you Soomla code, however once you are set up it slows down debugging other parts of your project.

So I added an option to CoreSettings to turn off the debug logs for Unity based code. It follows the same model as the existing native Debug Messages option. I had to change the wording of the original to highlight that the original is for native code only.