Create 'schema' config file on the root

[raulcf]

This 'schema' config file serves as a general configuration for all components. The different components of ver should be guaranteed to work together as long as they use the same "schema". What does this schema file dictate?

• the fields and data types of a profile. This should be indicated in such a way that is interpretable in Java (so the DDProfiler can use that info to understand what it needs to compute) in Python (so the dindex_store knows what to expect in the input JSON files and how to prepare the schemas of the target databases)
• may be also useful information for users of the aurum api, who would know what information is described in profiles

Later, we could have the ddprofiler auto configuring itself based on this schema file plus an 'adapter' file that indicates, for each attribute to compute, what analyzer to use to do so. I leave this comment here but indicate is explicitly outside the scope of creating the general 'schema' file. I also do not explain how to get the software to parse and interpret the 'schema' file.