Add insertions/frameshifts as branch labels

[rneher]

I added frameshifts and insertions to the metadata in ingest. these should be then part of the metadata once the next ingest has run. The idea would then be to

• collect all unique insertions and frameshifts
• assigned them as a binary characters to leafs
• do discrete state reconstruction on them (like the traits rule)
• for each branch, collect the events (separately for insertions and deletions) that map to it
• construct a label for insertions and deletions that can be displayed on the branch.

[corneliusroemer]

Write separate script using Augur ancestral/traits functions as a library.

• Build own characters
• Each unique frameshift/insertion gets a binary trait, binary vector
• Import mugration_inference frequency from Augur