Add ability to create SQLAlchemyObjectType with custom SQLAlchemyObjectTypeOptions

[nmvalera]

• Enables developers to create custom types that inherit from SQLAlchemyObjectType with custom SQLAlchemyObjectTypeOptions
• Enables developers to complexify the ObjectType inheritance tree starting from SQLAlchemyObjectType

[coveralls]

Coverage decreased (-0.3%) to 90.722% when pulling a830eb3 on nicolas-maurice:feature/custom-objecttype-options into 4827ce2 on graphql-python:master.

[coveralls]

Coverage decreased (-0.3%) to 90.722% when pulling 9206ec6 on nicolas-maurice:feature/custom-objecttype-options into 4827ce2 on graphql-python:master.

[coveralls]

Coverage decreased (-0.3%) to 90.722% when pulling 3e1b7fb on nicolas-maurice:feature/custom-objecttype-options into 4827ce2 on graphql-python:master.

[coveralls]

Coverage increased (+0.09%) to 91.065% when pulling 1840814 on nicolas-maurice:feature/custom-objecttype-options into 4827ce2 on graphql-python:master.