core: default 'include_in_backups' to negative of 'installed_by_rpm'
core: default 'include_in_backups' to negative of 'installed_by_rpm'

As we allow to backup template, even if installed by rpm, it makes sense
to not include such templates in backup by default.

QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin