Simplfy the data.sqlite3

[Christian-B]

Part of https://github.com/SpiNNakerManchester/SpiNNFrontEndCommon/pull/1207

Notes:

• This now writes a row to range data table even if the data read is empty! This allows distention between successfully read data of length zero (ok) and did not read any data (an error)

• The python side normally fills in the extraction table so that i just mocked here for unittests.

• getRecordingRegionContents is simpler that python because 1. It is just used for testing, 2. ByteArrayOutputStrea does not need to be setup with size.

[coveralls]

coverage: 36.964% (-0.04%) from 37.0% when pulling 43e58511edd84001aa5543be80826ed8792b5002 on extraction into c1e73f6b3e3e3ba927d31b6dbc3583c44363090b on master.