added optional descriptions to most parts of the activity json schema
start of support for BricLayer brix-topic dynamic value

Brix classes that support this need to implement a getEventTopic static method.

I've implemented that static method on a few Brix classes:
Callouts
Carousel
ImageViewer
LabelGroup
MultipleChoiceQuestion
Implement getBricTopic

unit tests are still needed.
Update d3 to version 3.3.7

https://github.com/mbostock/d3/releases/tag/v3.3.7
unit test BricWorks.getBricTopic
BricLayer dynamic value tests including for the new brix-topic type.
convert tabs to spaces, no other changes.
AMS w/ stub
Merge pull request #104 from lbondaryk/BirxInDiv_718

AMS w/ stub
activity schema dynamicValue now references all the defined types
Add quotes around property names that didn't have them in the activity config
changed tabs to spaces
Merge pull request #103 from lbondaryk/350-Hilight-mortar

350 hilight mortar (briclayer support for brix-topic dynamic value)