Give the user a hint to add the FrankConfig.xsd reference or add it automatically

**Is your feature request related to a problem? Please describe.**
When you open a configuration that doesn't have a reference to FrankConfig.xsd you will not have code completion in VSCode and Eclipse.

**Describe the solution you'd like**
Make it easy for the user to add it. Show a message that no reference was found on opening the file and ask the user whether the Frank!Flow should add it to the root element. The following needs to be added:
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="../FrankConfig.xsd"

**Describe alternatives you've considered**
Add it automatically when it is missing

**Additional context**
\-