(bug 44164) Add 'Portal' and 'Author' namespaces to iswikisource

This commit adds two new namespaces to the Icelandic Wikisource:
* 'Gátt' and 'Gáttarspjall' as 100 and 101, with English aliases
'Portal' and 'Portal_talk', respectively;
* 'Höfundur' and 'Höfundarspjall' as 102 and 103, with English
aliases 'Author' and 'Author_talk';
* Both namespaces are set to be searched by default per request.

Bug: 44164
Change-Id: I594dd822034ea80c5a177384deefc9bc59d000bd