ENH: Add more built-in convenience pipelines #304
Description
Following up on this comment by @danielballan , we need to complete the work of #250 and add built-in pipelines for as_grey, normalize, cropping, and as_rgb. In particular, as_grey is one of the most-used conveniences in pims and it must go in the next relese, with prominent documentation.
The trackpy walkthrough (and maybe other tutorials) also need to be updated.