osx: add 'make bundle' target to build OS X application bundle

creates application bundle claws-mail.app at $HOME/Desktop/

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
osx: add jhbuild moduleset file with dependencies to simplify claws-mail build

with this claws-mail could be build within preinstalled
gtk-osx env using following command:

  jhbuild build claws-mail_jhbuild.modules

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
osx: make sure that enchant modules are in bundle and could be found

patch relies on libenchant recognizing ENCHANT_MODULE_PATH env variable
to find moles location

Signed-off-by: Igor Mammedov <imammedo@redhat.com>