capture_jpeg should use capture_and_save internally

Currently:

• capture_jpeg saves a jpeg to disk and then returns a blob.
• capture_and_save saves a jpeg to disk.

However, capture_jpeg has its own implementation for capturing and saving to disk. Updating capture_jpeg to use capture_and_save will reduce repeat implementations. In theory this will allow capture_jpeg to be moved to the base camera.

Fixing this would close #299 (closed) and #355 (closed)