[core] force elevation for unprivileged users

* Using "highestAvailable" elevation allows standard users to run Rufus
  without being prompted for elevations, which prevents them from both
  detecting and formatting USB drives
* Since non administrator access is useless, switch to "requireAdministrator"
* Closes #153
* Also fix small issues with saving log and syslinux detection report
Merge branch 'master' into localization