Emap user queries

[jeremyestein]

Epic: #46

In conjunction with the DB design process, we will need to write some SQL queries that retrieve waveform data in a useful way, to check that they run in reasonable time and are relatively easy to write.
Since the DB design will likely be optimised for space/time efficiency rather than ease of writing queries, we may need to write some example R/python code to process the retrieved data into something the user would expect (unpacking the arrays mainly)