Initial changes to remove /boot/common

* find_directory() and hard-coded paths use /boot/system instead of
  /boot/common.
* The build system creates the writable directories in /boot/system
  instead of /boot/common.
* The build system no longer installs any packages in /boot/common.

data/system/boot/InstallerFinishScript

@@ -13,7 +13,7 @@ if [ ! -d "$target" ]; then
 	exit 1
 fi
 
-mkdir -p "$target/common/cache/tmp"
+mkdir -p "$target/system/cache/tmp"
 
 # remove Installer link
 rm -f "$target/home/Desktop/Installer"