Refactor samples structure and add tutorials

Put samples in Olingo git within the samples folder (e.g. “samples/tutorials/read”; “samples/tutorials/write”; “…”)
and do not include the samples folder into the project pom for the common build process (e.g. build samples only “on demand / manual” via a maven profile setting -> see example below).

This is based on discussion and decision on Olingo dev mailing list.