partners _newest tmaps should be dynamically generated

[StevenSong]

What
tensor_maps_partners_ecg.py contains definitions for twice as many tmaps than is necessary as each explicit tmap being defined twice, one for getting all ECGs in time series and one for getting newest ECG for each patient.

Why
the file is difficult to navigate and maintain, the conversion to a newest tmap is simple and can be done dynamically - similar method can be done for oldest

How
create a function build_partners_ecg_tensor_maps to create _newest or _oldest tmaps dynamically

Acceptance Criteria
functionality of _newest tmaps unchanged and tensor_maps_partners_ecg.py does not contain near duplicate tmaps