Read CZI image data from a existing pyramid level

[sebi06]

As a user of pylibCZIrw I want to be able to do the following things:

• learn about the existing pyramid levels of an existing CZI image (number of levels, scale)

  • This information is important to decide if the creation of a pyramid is really needed, e.g. the image is larger than sizeXY
  • sizeXY should be equal to the value that triggers a pyramid calculation in ZEN ideally
  • • see also PR feat: Add check pyramid needed (ie: if czi doesnt already have a pyramid, and is greater than 4096*4096) #52

• use this information to read pixel data from those levels

  • once the user knows about the existing pyramid levels there should be an option to directly read from existing pyramid levels