Class textbox

I am truly merging many features here. Let's list them:

• Modifications on the code from Clemens to allow also labelling textboxes. That implies changes on trained_annotation, user_labeling, plus many other files created for the definition of the blocktext features.
• Also, in user_labelling some functions were added to interact with Jordi's frontend
• The original Dash has not been modified, and instead there is a new Dash that works differently, and interacts with the backend.
• Also, there are some modifications on def_classes, preproc_doc, essentially because I found some errors in the creation of 04correctedxml.tar.gz Well, I do believe that it is.