Summary:
Adding conditional formatting rules feature.
Each column can have multiple styling rules which are applied in order
when evaluated to a truthy value.
- The creator panel has a new section: Cell Style
- New user action AddEmptyRule for adding an empty rule
- New columns in _grist_Table_columns and fields
A new color picker will be introduced in a follow-up diff (as it is also
used in choice/choice list/filters).
Design document:
https://grist.quip.com/FVzfAgoO5xOF/Conditional-Formatting-Implementation-Design
Test Plan: new tests
Reviewers: georgegevoian
Reviewed By: georgegevoian
Subscribers: alexmojaki
Differential Revision: https://phab.getgrist.com/D3282
