Much like the Web version, add support for labels.txt to training configurations.

Background Info:

• Labels.txt is added to a training command through This section of code in tasks.py
• The labels.txt file is a list of classification types that are going to replace or adjust the name of.
• This PR for the initial labels.txt importing may help: Labels.txt Upload #1072

Desktop Implementation:

• MultiTrainingMenu.vue will need to be modified to have a new optional file dialog. It can be null/empty or it can contain a text file
• When clicking on the file it should use openFromDisk('text') from here to load in the absoluate location of the file
• When running the Training the input arguments should be updated to include an option for the existence of a labels.txt file. This can be done in the viame.ts train() function where the arugment runTrainingArgs is of type RunTraining which as of writing this already has an option for 'labelText'