Use self.anchor to prepend plot IDs to make sure custom anchor is applied

[vladsavelyev]

Use self.anchor to prepend plot IDs to make sure custom anchor is applied
Helpful when module is run twice with a module_order config:

module_order:
  - fastqc:
      name: "FastQC (trimmed)"
      anchor: "fastqc_trimmed"
      info: "This section of the report shows FastQC results after adapter trimming."
      target: ""
      path_filters:
        - "*_1_trimmed_fastqc.zip"
  - cutadapt
  - fastqc:
      name: "FastQC (raw)"
      anchor: "fastqc_raw"
      path_filters:
        - "*_1_fastqc.zip"

In the result, instead of numerical suffixes in the JSON outputs:

"fastqc_sequence_length_distribution_plot": {
...
"fastqc_per_base_sequence_quality_plot": {
...
"fastqc_per_base_sequence_quality_plot-1": {
...

It becomes more clear which data belongs to which section:

"fastqc_trimmed_sequence_length_distribution_plot": {
...
"fastqc_trimmed_per_base_sequence_quality_plot": {
...
"fastqc_raw_per_base_sequence_quality_plot": {

Which is especially relevant for the sequence_length_distribution plot that would only be built for trimmed reads, and would always be skipped for raw reads due to identical sequence length.

Only fastqc module for now - WIP.

Fixes #2076
Fixes #2203

UPD: Should probably make it automatic, which requires #2036 to be completed first

[ewels]

Maybe we can do this prepending of the anchor to the ID in the table / plot code instead, so that people don't have to manually remember to do it.

Means we have to clean up the duplicated prefixes across all modules 😱 and where possible avoid changes in the resulting IDs, but hopefully not too bad..

[ewels]

Maybe fits nicely into the refactoring that we're doing for #1051