Add an observation_name_col parameter

[pinin4fjords]

Description of feature

The underlying issue @WackerO was trying to tackle in #62 is a mismatch between column headers of an expression matrix and the rows of a sample sheet. This can be more simply fixed by including the relevant data in the sample sheet (for example the bam file name output by featurecounts in the column header), and setting the appropriate observation_id_col in the workflow parameters.

The down-side of this is that all the plots etc will have the filenames, which is less than ideal.

Analagous to the existing feature_name_col, we need an observation_name_col that will allow us to use a different display name for samples than the one used in the expression matrix.

This will also require some upstream changes in shinyngs.

[pinin4fjords]

Added to the 1.1 milestone- I think this is important