GEOMESA-245 Allow multiple features to share a (set of) tables

* This pr adds a boolean hint to the UserData in a SFT.
* To share tables, we enforce restrictions on IndexSchemaFormat:
 Schema must start with a sharding partition and a constant string.
* Table code structure has been spun out.  A nascent structure of what it means to be a
 GeoMesa table is shown.
* Attribute like-eligibility has been enforced for the Attribute Index Strategy.
* A rough test for the AttributeIndexJob is provided.