JSON variable type implementation

[LouisMoreaux]

• update JS file for create and update proc variable
• update engine app package to get and set proc variable
• fix typo in migration script

[LouisMoreaux]

@commi235 @rallen2010 Adding a not on setting JSON process variable, I can't remember why but there is no public API to set a JSON process variable. Using the internal for now but we should discuss that

[commi235]

@commi235 @rallen2010 Adding a not on setting JSON process variable, I can't remember why but there is no public API to set a JSON process variable. Using the internal for now but we should discuss that

Can't remember why we skipped it. But I think adding a "simple" public setter makes sense.