IOS-1924 fixes: quoted text is black font color on black background composing a mail in darkmode (reply, forward)

IOS-1924 fixes: plain (non HTML) text mails not readable in dark mode (black text on black background)

IOS-1924 confirmed: light mode keeps working fine without tweaking anything (removed mods for light mode)

IOS-1924 stops changing link color (green should fit dark & light mode). Also experiments with default values for light mode.

IOS-2755 HTML takes care of light/dark mode automagically now (IF no font or background color is defined)