v1.5.0-1.sfos321

Changes

• Further downgrade the device dependency, this time from Requires= to Requisite=.
  Because all devices usable by mount-sdcard shall already exist and have a corresponding device unit spawned by Systemd, there is no need to let Systemd spawn new device units here (i.e., this is only relevant error cases, anyway).
  Plus, this may allow for intermittent, brief failures of a device to be ignored.
• Change license from MIT to LGPL-2.1-only.
• Add Before=umount.target to fully comply with Systemd's default dependencies for device, mount and path units.
  Note that this mimicry of a "standard" mount unit's behaviour by Conflicts=umount.target and Before=umount.target statements happens in addition to the (implicit) default dependencies of a "standard" service unit: Conflicts=shutdown.target, Before=shutdown.target, plus Requires=sysinit.target, After=sysinit.target and After=basic.target.