Update KDE Plasma to Plasma 5.21

[dominichayesferen]

It's coming out on February 16th, with the plan of having it in Feren OS in Plasma 5.21.2 if all goes to plan.

• [x] Wait for 5.21.2 to come out
• [x] Update patches
• [x] Update default settings for Vanilla Plasmoids
• [x] Remove GTK recolouring workaround now it's apparently finally fixed upstream
• [x] Make the Feren OS Applications Menu a thing
• [x] Port Kickoff fixes to it
• [x] Remove Simple Menu package
• [x] Add a first-login prompt for existing users to allow them to re-apply their Desktop Layout since it has changed
• [x] Add 'no' option to prompt that replaces the menu with Feren OS Applications Menu automatically and then leaves the user be
• [x] Replace Simple Menu with Feren OS Applications Menu in the Desktop Layout
• [x] Add in upstream pending patch to fix issues with Top Notch sized Plasma panels (https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/257)
• [x] Switch from Latte Dock to Plasma Panel for the Top Notch
• [x] Disable Latte Dock by default
• [x] Remove Latte Dock's default Feren OS layout
• [x] Switch from Latte Dock to Plasma Panel in default Desktop Layout
• [x] Rebase Feren OS Plasma Style on the latest Breeze (with A.P.T. patch included)
• [x] Support Margins in the Plasma Style
• [x] Support Adaptive Transparency in the Plasma Style (found https://bugs.kde.org/show_bug.cgi?id=434200)
• [x] Fix thicc 'solid' GTK 3 CSDs
• [x] Make KWin borders have new border
• [x] Give GTK3 CSDs shadows similar bordering
• [x] Backport Adaptive Transparency patches if that's even possible
• [x] Implement the scrapped Volume Meters design during 5.21 development into 5.21 if possible (sliders were there like 5.20 and the input levels were layered atop that in transparent text colour colouring)
• [x] Deprecate and remove the Kubuntu patched Global Theme (replaced by Breeze Twilight)
• [x] Update 'Vanilla' Panel Layout to match 5.21 defaults
• [x] Change the profile pictures in Users KCM
• [x] Update all layouts to use Margin Separators where needed
• [x] Replace GUFW with plasma-firewall
• [x] Update feren-kde-settings
• [ ] Try and add GTK Portal to the mix for Vivaldi and co. by default
• [x] Push Plasma 5.21.X officially
• [x] Close all bug reports labelled "Close after Plasma 5.21" since they're technically 'fixed'
• [x] Refresh Feren OS ISO

BONUS: [ ] Add option to themes to make them 'opaque' if blur is disabled - depends on https://bugs.kde.org/show_bug.cgi?id=430622 's fixing

[dominichayesferen]

Plasma 5.21.3:

• [x] Port patches over
• [x] Remove More Options non-working options
• [ ] Try and add GTK Portal to the mix for Vivaldi and co. by default