Reset license text if the user selects a suggested license expression

[meretp]

Is your feature request related to a problem? Please describe.
Whenever the user edited the license text for an attribution and afterwards decides to take one of the suggested licenses the license text is no longer consistent with the selected license.

Describe the solution you'd like
If the user selects a license expression from the dropdown, the license text should be reset such that the inferred license text from the selected license is displayed.

[mstykow]

Sorry @Hellgartner. Didn't see that you already grabbed the task. Hope you don't mind that I opened a PR.