Qtfred fixes and tweaks

[MjnMixael]

Fixes some things in QtFRED:

• Mission Stats message count was wrong
• Texture replace string algorithm was brittle
• Ship alt class heap issue crash on windows
• Match props menu item styling to the others
• Unify all up/down buttons to use the theme arrow icons
• Fix ship/wing dialog cues toggle buttons to obey they new settings
• Rename Objects to Object Orientation in the menu for clarity
• Fix menu separator color in dark mode

[wookieejedi]

This cleanup also looks good