fix: batch non-critical packages in single pacman call, drop old plasma theme, enable filesystem picker

Non-critical packages (Desktop/Plasma group, Utilities) went through try_install which installed them one-at-a-time (45 individual pacman calls). Override operation_try_install in PMPacman to batch all plain-string packages into a single call, matching the behavior of operation_install.

Also:
- Remove antergos-plasma-theme from rootfs (profile.yaml) and both netinstall Plasma groups
- Add allowFileSystemTypeSelection: true to both antergos and minimal partition.conf
- Both main.py files (profile + minimal) get the batching fix

iso-profiles/antergos/profile.yaml

@@ -31,7 +31,6 @@ rootfs:
     - antergos-welcome
     - yay
     - antergos-next-desktop-settings
-    - antergos-plasma-theme
     - pixie-sddm-git
     - antergos-wallpapers
     - antergos-grub-theme