Split up initramfs to make it smaller (Close #211)
Add generation of initramfs-extra with additional binaries
Extract both initramfs with pmbootstrap initfs extract
Add new splashscreens for missing partitions/files errors
Changes in init script:
- use busybox findfs applet to find boot partition
- mount boot partion
- extract initramfs-extra
- show error splashscreens accordingly and loop forever
- start usb unlock directly from unlock_root_partition (hook removed)
(Close #211 (closed))