SilentScreenshotter: Removed the dependency on Gdip.ahk lib + added checks for 'imgurClientID' and 'if Exist' for optipngPath
Now the script doesn't require gdip.ahk to be present (all the required functions were copied from there into the script's code).
The script is now taught to show a warning about absent 'imgurClientID', it also opens the needed URL (where the user can obtain it) and then stops the script.
Added 'if exist' check for optipng.exe. Although we use FileInstall on it - it is more reliable to run it with that check.