* restore missing build:css rule

* allow case-insensitive matches in project, context names

* allow more alternate syntaxes in filter expressions
- allow the syntax "(A)" to mean "pri == A"
- allow the operator "=" as an alternate form of "=="
- let quoted project or context names include ( or ).
- allow short forms YYYY or YYYY-MM to mean first day of year or month
  in date expressions, eg "due < 2021" means before 2021-01-01.
- allow the syntax "due:DATE" to mean string match due date
  against prefix DATE,e eg: "due:2021" means due date begins with 2021.

* simple text color feedback for query validity

* bug fix to the due:DATESTR feature