[1.7] Modifying a blocks "isotropic" is no longer supported

Verification builds:

1.7.0.2 Release 1117901

Summary:
The isotropic variable within the blocks.json are no longer having affect on blocks 

Impact:
This affects the Tiny Footprints texture pack, Adventure's Dream texture pack and multiple content of ours. This will also affect future content too. This is a vital feature for us. 

Repro Steps:

1. Download the Adventure's Dream Mashup pack from the Store
2. Create a new world with the pack equipped and have Cheats enabled
3. Type the command /give @s red_sandstone 16
4. Create a 4x4 grid of the red sandstone
5. Observe the rotation of the texture 
6. Repeat in a 1.6 build and observe the texture displaying as intended 

Observed Results: 
Modified Isotropic variables are no longer being read and thus some textures no longer have the correct designed appearance.

Expected Results: 
Modified Isotropic variables are continued to be supported/backwards compatible 

Screenshots/Videos attached: 
Yes

Regression Build:
1.6 builds. Confirmed in 980905