Improve storage efficiency

[jeremyestein]

Currently using DOUBLE PRECISION ARRAY. Could use NUMERIC ARRAY instead. Most streams have values with not many digits in them, so NUMERIC ARRAY with low parameters could be quite efficient. If some streams have more digits in, consider using separate "big" and "small" waveform tables to maximise storage efficiency (at some cost to user friendliness - could be improved with an SQL view that is the union of both tables?)