Implement capture steps from appnote

[jepler]

Section 4.11 of the appnote https://www.arducam.com/downloads/modules/OV5640/OV5640_Software_app_note_parallel.pdf explains the sequence of operations to switch between preview mode & capture mode, correctly exposing the capture.

Implement it, so that a "capture_jpeg(buf, jpeg_resolution)" method can be called. It performs all the steps, including setting back to preview mode, and returns the jpeg image data.