title: Create spark dataframe schema from json schema representation
body: <p>Is there a way to serialize a dataframe schema to json and deserialize it later on?</p>
  
  <p>The use case is simple: 
  I have a json configuration file which contains the schema for dataframes I need to read.
  I want to be able to create the default configuration from an existing schema (in a dataframe) and I want to be able to generate the relevant schema to be used later on by reading it from the json string.</p>