whonixcheck: do not start whonixcheck, if whonixsetup hasn't finished yet
whonixsetup: start whonixcheck at the end of whonixsetup on Whonix-Workstation
code simplification
build script: using guestmount, guestunmount/fusermount for mounting/unmounting instead of manual mount/unmount commands
Moved help-steps/mount-vdi, help-steps/unmount-vdi and help-steps/unmount-vdi-force to whonix-developer-meta-files/debug-steps.