Issue #115: add script for filtering pdt/v-vallex files

Filter functionality (solution to issue-#115)

1. Prepared simple script that creates filtered versions of pdt-vallex.* and v-vallex.* files according to units present in the n-vallex-shared.* and NomVallex.* files

2. Prepared general filter functionality (frontend+backend) that enables to filter loaded files according to units present in the given query. The extracted units are searched in adjustable attributes and can be filled with all the remaining LUs of the matched lexeme.

TODO:

• when creating the filtered files using web client the progress bar is jumping/shaking (weird scrolling)
• better testing
• change icon in the Sidebar to something more intuitive