Fix for Issue 8

This is a proper fix for #8.

If a gma is locked, prompt the user if he wants to open it in ReadOnly Mode. In ReadOnly Mode, all buttons, which would write sth into the stream, will be disabled (but visible :smile:).

ReadOnly opens the FileStream with just Read-Access.
( I didn't know, if we should grant FileShare permissions, since Gmod could interrupt it somehow, need some further investigation on this)



If you want to change something, feel free to do so :smiley: 
Johnny