* M12: board templates and tables
Five built-in board templates (retrospective, brainstorm, weekly planner,
flow chart, kanban board) placed as ordinary board objects in one undo step
(board.template, board.templates) from a toolbar picker with pictures, and
board tables made of auto layout frames (board.table, board.tableEdit; up to
50 x 20), typed into with a double-click and edited by row and column from
the bar over the selection. Docs: boards-parity, gap 24, ROADMAP, mcp.
* M12: board templates picker on egui 0.37
Id::new and Ui::id are deprecated in egui 0.37: the templates picker's area uses Id::unique, its buttons' interaction ids come from ui.scope_id(), and its test reads the board bar's area by Id::unique.