Change default adapters file in Trimmomatic steps dialog depending on the current library mode

It is possible to select single-end or paired-end reads in the "Improve Reads with Trimmomatic" element (the "Input data" attribute). The default path to adapters should depend on this attribute.

This path is in the "Configure Trimmomatic Steps" dialog (you can call this dialog from the custom delegate of 'Trimming steps" attribute) in the settings widget for ILLUMINACLIP step. "data/adapters/illumina/TruSeq3-SE.fa" should be set by default for single-end reads and "data/adapters/illumina/TruSeq3-PE-2.fa" should be set for paired-end reads.