Add an Mapman overview plot

[asishallab]

In the latest Mapman 4 ontology there are 27 root bins - plus two not manually curated ones.
The latter are Bin 50 and Bin 35.

It would be nice to have a new plot, that is a collection of 27 horizontal boxplots.
Each boxplot shows the distribution of numerical values selected from the info table for transcripts having the respective
root Mapman Bin.

Input form - takes inspiration from the input form of the enrichment analysis:
Enable to select an info_table column for the numerical values that go into the boxplots, e.g. log-fold-change between control and cold stress treatment.
Enable to select the column that holds the Mapman Bin identifiers and a separator char (like in the enrichment analysis). Use default.
Enable to specify a list of transcript (gene) identifiers to subset. This can be either entered manually (one Gene ID per line) or by a selector. Again like in enrichment analysis.

Plot:

• see screenshot for a crude example
• Replace BINCODE with NAME
• Put the number of genes annotated with a root bin next to the y-axis labels
• note that "value" is log-fold-change of S. lycopersicum control versus cold stress treatment in this case