Fancy Flymake mode-line construct displays status

Fancy Flymake mode-line construct displays status

Imitates compilation-mode's mode-line a bit, and uses its faces.

* lisp/progmodes/flymake.el
(flymake-error, flymake-warning, flymake-note): Add
mode-line-face to these flymake error types.
(flymake-note): Notes don't need a noisy fringe bitmap.
(flymake-lighter): Delete.
(flymake--update-lighter): Delete.
(flymake--mode-line-format): New function and variable.
(flymake--diagnostics-table): New buffer-local variable.
(flymake--handle-report): Don't update "lighters".  Affect
flymake--diagnostics-table.
(flymake--run-backend): Init flymake--diagnostics-table for backend.
(flymake-mode): Use flymake--mode-line-format.
(flymake-mode): Don't update lighter.
(flymake--highlight-line): Be more careful when overriding a
nil default overlay property.