when switching modes/camera set flash accordingly

[CristianoCastro]

When switching camera/mode, the current flash mode should be set if device supports it.

Example: If I start in video mode with back camera and set flash on, then switch to front camera (which doesn't support flash), then switch again to back camera, flash is off when it should be on, and the internal _flashMode camera is still PBJFlashModeOn.