Update validator's tests to DTS version `1.0`

[mromanello]

As pointed out by distributed-text-services/MyDapytains#16

[mromanello]

• update all examples according to the examples in the DTS specs (1.0).
• Update version in "$comment" of all schemas
• ensure that a 400 error is raised when querying the Navigation endpoint as described in this issue
• raise a warning instead of an exception when HTTP responses don't contain Content-Type: application/ld+json as per this issue
• check that " dts:extension MUST have a @context property providing the definition of terms that are not included in DublinCore vocabulary" – raise a warning if absent.