Change order of validation steps

Execute validation formula *before* validating dataformat.
This allows validation formula to massage the submitted value.

E.g. to make a Number field accept input like "0,2", without requiring
a side-car Text field/item pair.
Tidying and TODO notes
Merge pull request #409 from plomino/jean-reorder-validation

Change order of validation steps
Merge pull request #411 from plomino/jean-tidying

Tidying and TODO notes
Merge pull request #410 from plomino/jean-getColumnRender

Create `getColumnRender` method on view
Fix #415
Deal gracefully with missing value
Use getColumnRender for sum also
Merge branch 'github-main' of github.com:plomino/Plomino into jean-getColumnRender

Conflicts:
	Products/CMFPlomino/PlominoColumn.py