- added PHP utility function to check for file name validity
- fixes issue where a user can create a file called ".." from the files UI
- added extra checks to make sure newfile.php and newfolder.php also
  check for invalid characters

the only problem that I found with it so far is that it gives a database locked error on login,
the rest seems to work fine but more testing is required.

Start of the refactoring. Commit is quite big because I forgot to use git right from the beginning. Sorry.