Corebird: Create corebird folders before accessing the database

This fixes a bug which led to totally unsafed changes when first
running corebird.
Corebird: Don't create MainWindow instance with null account

This previously led to a running corebird process without an open window
when the user first created and initialized an account, then opened
an window for it.
PKGBUILD: Update to pacman 4.1 standards

Thanks to grawity