PackageFSMountType: Add *_ENUM_COUNT
packagefs: Add a .settings package symlink

It points to the settings directory appropriate for global settings.
When a package is installed in ~/config, we cannot use the settings/
subdirectory for global settings, since then the files could clash with
equally named user specific settings files (e.g. in case of
ssh/known_hosts). So we use ~/config/settings/global for global
settings instead.
Add AddPackageFilesToHaikuImage rule
Simplify use of InstallOptionalHaikuImagePackage

When invoked for a hpkg only the installation location (i.e. "common"
or "system") has to be specified now and "common" is the default. The
rule uses AddPackageFilesToHaikuImage now.
Pimp up AddTargetVariableToScript to support a list of targets
BStringList: Add Join()
package list: Add option "-p"

It prints just a list of paths for all entries.
Extract packages' settings dir to common/settings in image

That's a somewhat crude initial approach to installing the default
settings of packages when building the image.