default urwid bright-is-bold false

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I've noticed urwid looks strange since I've started using "kitty" terminal. kitty comes with its own custom termaps, and so it's necessary to set `TERM=kitty`. In urwid, rather than using termap, they use a simple "not xterm" heuristic for their "bright is bold" flag. This results in a random half of all syntax becoming bold.

https://github.com/urwid/urwid/blob/master/urwid/raw_display.py#L79

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Could we call `set_terminal_properties(bright_is_bold=False)` during startup? If you want to get fancy we could determine this boolean via termcap (as urwid should have done).