stable_id_version setter/getter for core object types, sets stable_id with a . delimited version or fetches stable_id with .version concatonated (if version is set)

- handlers in Exon, Gene, Operon, OperonTranscript and Transcript Adaptors for a versions fetch_by_stable_id call and new handler for fetch_by_stable_id_version
- Translation is handled implicitly through calls to Transcript
- Test cases for the new handlers and functionality

returns exon rank relative to an input transcript

This reverts commit 856a5aa2.

not available with default installation
will come back under another form

Due to changes in BaseFeatureAdaptor we need to save the state of
meta_coord otherwise a number of tests will begin to fail. Same is
true of xref.

cdna_coding_end(), coding_region_start(), and coding_region_end() on
exons.

Current API and test DB passes the tests.

added exon test - failing because CloneAdaptor is not to spec! Start of the testing and bug hunting ...