MB-Lab: Add a simplified export expression feature

[amirpavlo]

This feature makes use of Shape keys. The work flow is:

1. Create a character
2. Create a basis shape key followed by as many shape keys you desire
3. Once you're done click on the "Export Expression Shape Keys" 3a. Optionally you can select the "Apply to all Phenotype". This will apply the shape keys to all the expression files for all the same phenotype.

Signed-off-by: Amir Shehata [email protected]

[TetoTheSquirrelFox]

Many many thanks for the helps. Just 2 things about your commit :

• You add indent to file_ops.save_json. No, please, because this method is used by all .json files and for some files it gives an ugly result, plus for a reason, in some tools the method doesn't work (the file is not written and an exception is shown).
• I would say "import shapekeys" instead of "export shapekeys" for the button because you import to MB-Lab.

[animate1978]

Unfortunately this pull request causes conflict somehow and I am unable to fix this on my end, using the 'dev' branch.