Makefile: Add common library to build dependencies

Add "lib/common.sh" to the build dependencies of our scripts to ensure
everything gets rebuilt when we modify a common function. Also, add
"Makefile" itself to enforce a rebuild if the edit command changes.

Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>
Signed-off-by: Pierre Schmitz <pierre@archlinux.de>