Create better support for license expressions

[mstykow]

Is your feature request related to a problem? Please describe.
As a user, I want the option to enter more than one license per attribution and specify relationships between them.

Describe the solution you'd like
Create a mechanism to add and remove input fields, one for each license name, and operators between them. Additional licenses should not support custom license texts, only the first one does. Then, use SPDX license expression syntax to concatenate the license names on saving. Also parse concatenated license names from the input file to display them separately.

Additional context
At the moment, the user must know that licenses can be concatenated using "AND" or "OR".

https://spdx.github.io/spdx-spec/v2.3/SPDX-license-expressions/

[benedikt-richter]

Related issue: #970