Prefetch the list of fonts for the style editor dialog

On my machine (with ~5000 fonts installed), enumerating the installed
fonts was about 75% of the total construction time of the style editor
dialog.
Load autoloaded automation scripts in parallel
Kill AssDialogue::SetMarginString

It's no longer used anywhere.
Kill AssDialogue::GetMarginString

It didn't actually make the calling code any shorter or simpler.
Fully extract the resolution resampling logic from DialogResample
Fix display of Unicode font names in the fonts collector dialog
Remove pointless wxID_CANCEL binding
Also handle wxID_CANCEL in DialogManager

wxEVT_CLOSE_WINDOW is only triggered from the platform's close buttons,
not cancel buttons/ESC, so modeless dialogs closed in that way were not
getting deleted.