Classic CSS tweaks for Thunderbird Quantum v1.1.0

[GENERAL]

• pre-configured for Thunderbird 78+
• my_userChrome.css / my_userContent.css files get imported automatically, if present

[Buttons]

• (tweak) Tb78+: classic button appearance for main toolbars
• (tweak) icon sets (Tb 1, 2, 3...) do not affect folder icons anymore
• (new) icon sets (Tb 1, 2, 3...) for folder icons (not compatible to dynamic folder colors)

[Appbutton]

• (fix) alternative/classic appbutton appearance
• (fix) icon only (different icon versions)

[GENERAL UI]

• (tweak) Menubar: position above/below tabs (default/Aero) + border
• (new) lw-themes: extend lw-theme to Quick filter bar and messenger box (if, supported by lw-theme)
• (new) transparent mail header: mails for lw-themes (if, supported by lw-theme)

[Add-on manager]

• (new) Tb78+: alternative appearance (default/Aero)
• (new) Tb78+: compact and more compact modes
• (fix) recent updates category always visible

[Preferences in tab]

• (new) Tb78+: alternative appearance (default/Aero)
• (removed) 'old' alternative appearance (default/Aero)