Use tagged value to determine model package for imvertor

[GeertBellekens]

As an alternative for using a specific stereotype to determine which package is an imvertor package and thus should trigger showing the add-in window the addin should use a tagged value.
If a tagged value exists with the name "imvertor" and value "model" then that package should be considered an imvertor package.
The existing mechanism using the stereotypes should remain for the time being.

[GeertBellekens]

fixed in version 1.4.1.0