feat: publication-style pileups visualizations

[deliaBlue]

Modify the ASCII-style alignment pileups aesthetics to create publication-style publications.

First, filter the pileups with the arguments:

--min-count: minimum count for a sequence to be kept. Default: 0

--max-sequences: maximum number of sequences with the highest counts to be displayed. Default 30.

--keep-all: keep pileups even if it has no mapped sequences.

Right now, MIRFLOWZ runs the pileup script three different times: once per library, once per run and (if specified) once per group. Therefore, in order for the user to set a custom counts threshold, the configuration file will include two new parameters, in the form of dictionaries: min_counts and max_sequence. These new dictionaries will have as keys per_lib, per_run and per_group, and as default values the ones specified above for the parameters --min-count and --max-sequences respectively.

Then, create HTML files to visualize the pileups and its corresponding CSS files.