Automatically add the `-n` flag to `hic_juicer_tools_pre_ext_args` when the HiC assembly mode is true

[GallVp]

The parameter was added as hic_assembly_mode. When assembly mode is set, the matrix normalisation fails. Therefore, it is recommended to set the hic_juicer_tools_pre_ext_args parameter to -n to skip normalisations.

Originally posted by @GallVp in #219

It is also preferable to print a warning message and explain the reason.

[ignacio3437]

I vote for this solution:
When "hic_assembly_mode" = TRUE then "hic_juicer_tools_pre_ext_args": "-n"

Is there a reason for this not to be the default behavior? Why would the user want assembly mode without -n turned on?

Printing a warning would be good as well.