Add some license keys to the common licenses list

[DennisClark]

Apparently the *gpl-n.n-plus (the “or later” licenses) are not considered common licenses by the aboutcode-toolkit attrib process. This has resulted in lots of extra license texts in some recently generated attribution documents. Please add the following license keys to the common licenses list:
gpl-1.0-plus
gpl-2.0-plus
gpl-3.0-plus
lgpl-2.0-plus
lgpl-2.1-plus
lgpl-3.0-plus
agpl-3.0-plus

[DennisClark]

Fix confirmed in the develop branch. Thanks.