Adapt examples, extend schemas and add schemas

[DunklesArchipel]

This rather large PR contains schemas for all example files and adapted example files (except the example which combines the files)

I adopted JSON schema draft-06 (hopefully) in all cases.

In a previous PR by @linuxrider changes were made to the system schema which are rather useful. We should consider these in the development of echemdb and update all entries in the repository:

• system.electrodes is now a list and the system.electrodes.number_of_electrodes has been removed.

This PR does not yet include schemas to verify the input files for svgdigitizer or to verify the echemdb datapackage. These have to be constructed from the different blocks.

I also do not know yet how to combine two schemas, i.e., echemdb schema with frictionless schema.

We should discuss how to proceed.

[DunklesArchipel]

The readme should be updated (see #25 )

[DunklesArchipel]

Recent updates include a number of changes. Furthermore, there is now an example file for local metadata generation with autotag and svgdigitizer.