make_module_sequence_dict should filter out peptides that are all underscores

[tobsecret]

Observed behavior:
Sometimes when using collect_aa_sequences, some accession numbers cannot be found or the phosphosite is incorrectly annotated for the corresponding accession, resulting in a string of underscores being returned.

phosphodisco/phosphodisco/classes.py

Line 521 in 90460e4

def collect_aa_sequences(

Expected behavior:
make_module_sequence_dict should filter out peptides that are exclusively underscores, maybe even provide an option to filter out ones that have more than 50% underscores.

phosphodisco/phosphodisco/motif_analysis.py

Line 68 in 90460e4

def make_module_sequence_dict(