Inject-LogonCredentials bug fixes & rename

Inject-LogonCredentials has been renamed to Invoke-CredentialInjection.

Added a check to ensure the script isn't being run from Session0 with
the "NewWinLogon" flag. This flag does not work in Session0 because
winlogon.exe tries to load stuff from user32.dll which requires a
desktop is present. This is not possible in Session0 because there is no
desktop/GUI, so it causes winlogon to load and then immediately close
with error code c0000142 indicating a DLL failed to initialize. There is
no way to fix this that I know of, if you need to run the script from
Session0 use the "ExistingWinLogon" flag.