Add infrastructure and fix minor issues

[jaysneg]

Implementation of:

• Infrastructure SDO & relationships
• Fix process_relationships processing for TTP-to-TTP relationships
• Fix attack pattern relationship typo

[rpiazza]

Hi @jaysneg,

Thanks for this pull request! I'm sure we will incorporate it into the slider when we update it to handle the latest working draft of the STIX 2.1 spec!

[jaysneg]

Hi, is there any TODO list for STIX 2.1 support?

…

On 27 Dec 2019, at 15:41, Rich Piazza ***@***.***> wrote: Hi @jaysneg <https://github.com/jaysneg>, Thanks for this pull request! I'm sure we will incorporate it into the slider when we update it to handle the latest working draft of the STIX 2.1 spec! — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#42?email_source=notifications&email_token=AAGSKZZSECXEWOJMVXYOMDDQ2YAXRA5CNFSM4J67MK62YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEHXGTPY#issuecomment-569272767>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAGSKZ3P37WGNGFK6SAUG7TQ2YAXRANCNFSM4J67MK6Q>.

[rpiazza]

@jaysneg

No formal TODO list... Probably in the new year I will just put out a new version to conform to the latest working draft - which should be the final version of 2.1

[rpiazza]

Similar changes made in other commits