fixed typo

Signed-off-by: Manuel Traut <manut@linutronix.de>
GUI: check version number input validity and limit it to 25 chars

Signed-off-by: Manuel Traut <manut@linutronix.de>
updated: downgrade to old versions, pre/post.sh handling

pre.sh and post.sh scripts are executed now on update start and end
the current and target version numbers are passed to these scripts
remount of readonly partitions when updating is working now

Signed-off-by: Manuel Traut <manut@linutronix.de>