Split happy data into INDEL and SNP tables

[sophie22]

• This comment contains a description of changes (with reason)
• CHANGELOG.md has been updated

This is an attempt to resolve issue #1233
Data from the happy file is split into indel_data and snp_data and presented in separate tables in the report to allow for different thresholds to be set during conditional formatting set in the config file. Column headers now have an '_indel' or '_snp' suffix, so that they can be referred to in the config file.
Potential future improvement could include an option set in the config file whether or not to split the happy values.

[sophie22]

It's not failing the automated tests but it also doesn't show the data in the actual report for the split tables right now

[sophie22]

Stuck on trying to figure out what 'headers' mean in the table.plot(data, header, config)
and how to have the data column headers the same (so that data is correctly put into both tables after reading in the file content) but the HTML header tags named differently for indel and snp so that they can be referred to using different col_header names in the config file.

[sophie22]

had to change the headers when storing the file data into separate dicts so that later on they are different and generate unique HTML tags (which can be used in the config file for conditional formatting)
might not be the neatest way but it works now and passes the automated tests as well

[ewels]

Looks great! Tested locally and working perfectly 🚀

Thanks for the contribution, and sorry for the slow review / merge.