definition and definition-type properties are deprecated with implications for STIX 2.2

[rpiazza]

definition and definition-type properties are deprecated in STIX 2.1. If they are removed in STIX 2.2, then it would not be possible to define statement and TLP 1.0 data markings in STIX 2.2.

As TLP 1.0 is being replace by TLP 2.0, the STIX ids defined for TLP 1.0 in the specification could still be used. However, it would be incongruous to use STIX 2.1 to express new statement data markings.

With the addition of other data markings, such as IEP, PAP, ACS, CUI (via extensions in 2.1), the data marking object should probably be redesigned in 2.2