[WIP] (api) Follow xAPI spec for versioning

[Leobouloc]

WIP

Purpose

In link with : #424

Ralph currently does not follow the xAPI spec for versioning. It is proposed to implement:

• The LRS MUST include the "X-Experience-API-Version" header in every response.
• The LRS MUST set this header to the latest patch version.
• Statements returned by an LRS MUST retain the version they are accepted with. If they lack a version, the version MUST be set to 1.0.0.

Proposal

• answer question: are the proposals above compatible (answer: https://github.com/adlnet/xAPI-Spec/blob/master/xAPI-Data.md#learning-record-provider-requirements-2)
• add version to response header
• test response headers for get, put, post
• add version to statement (get)
• test that version was properly added
• parametrize version