Disable backslash escaping in echo

In shells where echo backslash escaping is enabled by default
the EFI paths (backslash-delimited) get badly scrambled.
Some variable quotting added
Use -u instead of -@ to pass EFI loader arguments

We need those encoded in Unicode
Remove and re-add each boot variable

efibootmgr --bootnum does not work as advertised – it doesn't
modify boot variable.
@EFI_PLATFORM_PATH@ macro for us in $ARGS

Linux kernel EFI stub requires absolute EFI path to the initrd,
this way we can set it without hardcoding the $PLATFORM_DIR
'kernel' and 'kernel-old' modules added
Version: 0.2