* Fix#145: add deviceinfo_flash_offset_base again
* Add default OFFSET_BASE value in flasher if deviceinfo_flash_offset_base variable is not set
...and set correct default base value in create_bootimg function
* allows to build/extract/list initramfs, add/del hook
* rebuild the initfs whenever running install or trying to flash/boot it
* flasher flash/boot: automatically set up a minimal rootfs with kernel and initfs,
if it does not exist yet