Dataset validation

[martukas]

When uploading a dataset, the server should perform some checks before adding it to the database:

• uniqueness - this can be ascertained by filename, which should be fairly unique by virtue of the seconds-resolution timestamp, but because it includes the tester's name and scenario name, it is virtually guaranteed to be unique
• identification of device being tested. There should be a device profile in the database describing the prototype being tested. Similar requirements could be applied for test equipment identification.
• some sort of schema to check that json structure is as expected?

[martukas]

It may be useful to reimplement the database module before doing this as described in #12