Dcml annotation parser

[manoskary]

Import for DCML corpora tsv files

DONE

• functional import with the possibility to include only notes, or notes, measures and harmony.
• Added optional dependency in pandas
• Some updates on score classes such as Cadences, Roman numerals and Phrases.
• Updated the estimate symbolic duration function in music.py.
• Move globals from partitura.utils.music to separate script called partitura.utils.globals to avoid circular import errors. (This will be done in a following PR after this one is merged to not break other components).
• Included infer root note, bass note from Roman Numeral and Chord Symbol strings.
• Included validity checks for Roman Numeral Symbols and Cadence types.
• Updates and fixes on note transposition

TODOs (For new PRs)

• Remove pandas dependency:
  This will be planned for later using numpy.genfromtxt. It can be done but the process is much more complicated because it transforms many strings to byte strings and it will take some major restructuring. For now the code raises a warning that pandas is required. For the future, we replace with numpy.genfromtxt and replace the warning. A relevant Issue will be opened.
• Notebook and github discussion with documentation about RomanNumerals and Intervals and such

[fosfrancesco]

The PR is good, I'm requesting some cosmetic changes for better code readability.