[iso] fix handling of label-based ISOs

* Linux has a MAJOR quirk in that labels such as "Contains Space"
  get converted to "/dev/disk/by-label/Contains\x20Space".
* While Rufus already had smart label Syslinux handling (by replacing
  the ones found in isolinux.cfg to their more limited FAT32 version)
  there was absolutely NO WAY of guessing this quirk until ISOs
  such as Red Hat 7 or CentOS 7 started to use spaces in their ISO
  labels and people reported breakage!
* This commit also fixes an issue where psz_fullpath was modified when
  it shouldn't, which broke Debian 7.7.0, and most likely any ISO
  containing a subdirectory in the directory where a syslinux/isolinux
  config file is located.
* Closes #396
* Closes #394
* Closes #388
* Closes #380
[net] add platform to user agent when checking for updates

* Also update Windows version strings for Windows 10
* Also set rufus-next to 1.4.12
* Closes #393
Fix Czech translation

* Closes #395