LAB01-03 : Some fix on instructions

[massimobonanni]

LAB01:

• The name of the file to use for test is a pdf not a png.
• The language options must be enabled in the Analyse option, otherwise there is no indication of the language in the result.
• Optimization in the code (C#).

LAB03:

• I added the name of the documents to use for the first labeling because the order of the training documents can be different from the alphabetical order in the labeling tool.
• Add the full name of the butto to add a new field instead the simple +.