Part of issue #862 - Add `beef.debug()` for client-side debugging

Add `beef.debug()` function - wraps `console.log()`

Debug messages are suppressed for browsers which don't support `console.log()`

Update './core/*' to use `beef.debug()` instead of `console.log()`
Update './modules/*' to use `beef.debug()` instead of `console.log()`
Update './extensions/*' to use `beef.debug()` instead of `console.log()`

Add 'modules/debug/test_beef_debug/' module