allow initializers to run even when phpcr-odm is not present

fix #83 

test coverage is probably not that big, but i tested things locally and we still execute both parts when we have phpcr-odm present. and we will quickly see on travis if we broke something.

i fear there might be other places where we fail if phpcr-odm is not present - ideally we would have a test suite that we could run on travis without having phpcr-odm installed.