Small [usefull] changes

[tonirv68]

I have developped locally several improvements:
Button "Select All tags match filter" and "unselect all Labels", usefull if for instance you have selected "cell phone" and you want to made replacements in every label (much faster than "all the labels")

And also I have introduced two new functionalities:

• Remove special chars from tags
• Pre-filtering tags; I think this is very usefull if you want to keep a big dataset folder structure and edit tags based on certain values, for instance: "mirror,reflection" , then, only images with that labels are loaded. (Only for load, then you can remove the labels and the image remain loaded)
  

The problem is that I am not an expert in python nor in shared git repositories... I do not know how to colaborate, if somebody feels that this is interesting, put a comment