Fix shared access flags usage XFile::Open | file monitor notify when size changes | removed delayed texture update | added some checks

Those flags are somewhat misleading , took me a while to figure out why I couldn't open for read a file that is already used by another process. 
We need FILE_NOTIFY_CHANGE_SIZE to get a change notification when working with files already used by another process. It's still not perfect tho.
Added necessary checks for text from file (Open/ReadFileToString cases); removed texture update delay as I consider it unnecessary.

(sorry for the revert screw-up)