Added possibility to define custom action links and properties in differential.

Summary:
There was a need to add old facebook specific action links and properties
back to differential.

Test Plan:
Tested that all the facebook specific links work for multiple
different revisions.

Reviewed By: epriestley
Reviewers: epriestley
CC: jungejason, tuomaspelkonen, epriestley
Differential Revision: 127