Update interpolate to use numpy instead of deprecated scipy interp1d

[mmcauliffe]

Currently Interpolated track uses the legacy interp1d:

PolyglotDB/polyglotdb/query/annotations/attributes/acoustic.py

Line 256 in c63831a

f = interpolate.interp1d([float(x1) for x1 in x if data[x1][o] and data[x1][o] > 0], y)

.

We should change this to use numpy.interp.

[massimolipari]

While we do this, it would be good to add functionality to round formant measures to 2 decimal places, as is already currently done in, say, polyglotdb/acoustics/formants/multiple_num_formants.praat. This would help keep file sizes down when querying.