Merge livecd-creator and image-creator

image-creator was duplicating a lot of code, while still failing to stay
in sync with livecd-creator (not providing useful options, such as
tmpdir or cachedir). Make it a link to livecd-creator and determine the
image packaging by argv[0].
Do not disable SELinux labels if run in permissive mode
Do not use local mke2fs feature configuration to determine flags for ext fs

It could have features not desirable or supported in target system;
hardcoding them is a bit more robust.
Fix a typo
Add support for creating and mounting FAT filesystems
Add possibility to set up a loopback device with size and offset

Useful for partitions. Also, we can't touch the underlying storage then,
treating the loopback volume as a physical disk partition.
Add partitioned disk creator
Make is possible to create a multi-partition image with MBR table
Install GRUB bootloader