Addressing metrical concerns in JAMS annotations

[jonnybluesman]

Main problem

Users currently need to reference and use the original score / symbolic content to fully make sense of the annotations. This happens every time users need to manipulate metrical content in the symbolic partitions. Also, starting times are not consistent, as some of them use 0 as initial measure / beat number.

Affected partitions

Schubert Winterreise, Real Book, Wikifonia, iReal Pro, BiaB, When in Rome, Rock Corpus, Mozart Piano Sonata, Jazz Corpus, Nottingham

Related issues: #53 #52

Proposed solution

Addressing this issue requires a number of interventions, including the following.

• Measure and beat onsets should always start from 1;
• A new namespace is introduced for time signature (wrapping also changes);
• For now, until we will start working on JAMS Score / JAMS X, durations are always encoded in beats (and not quarter beats).

Additional related tasks

• Bug-check and fix on the iReal Pro partition (key starting from measure 1);
• Include missing metadata.