Filename normalize rules & behavior changed

[hranicka]

I think that _normalizeFilenames should be turned on by default because user shouldn't create invalid file and directory names.

I changed behavior of normalizer like this:

• uploader::checkFilename() doesn't check for regexp -> when we change normalizing function, the previous implementation of checkFilename had own rules and caused problems even when filename had right format given by normalizing funcion. I think it's normalizer response.
• file::normalizeFilename() uses more robust and better implementation derived from Nette Framework
  • it translates all names to URL-friendly format, the previous implementation failed eg. on czech diacritics
  • eg. "nová složka" from user's input will be saved now as "nova-slozka" (URL-friendly)