CLEM database tables need to be updated

[tieneupin]

Now that we have a better of what the CLEM workflow should be, the tables and columns will need to be updated

CLEMImageSeries and CLEMImageStack

• Image alignment to happen in stages:
  1. Align to self, then
  2. Flatten the image stacks (if desired)
  3. Align to a reference stack
• If possible, try and keep aligned images in memory, and save only the final product
• Individual RGB images do not need to be created; columns can be removed
• Bright field + fluorescent and fluorescent-only composite images are desired; create a separate database table to register these files (CLEMCompositeImages?)

[tieneupin]

PR #430 removes the unused database columns.