Function for file validation

[werpuc]

As we (usually) allow the user to upload his own data file, we need to check its content.
The file cannot contain:

• empty lines - it can interfere with the workflow
• forbidden symbols - how they should be replaced?

[michbur]

Which symbols are forbidden? Do we forbid UTF-8?

[werpuc]

This should be discussed - but the aim is to limit overly creative names e.q. state names, as we experienced before. To begin with, I think that polish letters are definitely a no-no.