Disable VisualEditor in content namespaces on svwiktionary

We tried to only enable it in the User namespace, but the way the config
was rigged up, the main namespace was added because it's a content namespace.

Adding a flag to disable adding content namespaces, and only setting it
for svwiktionary.

Bug: 57356
Change-Id: Ie190a5853d5e17760cb6616dbaf9f3b2da4fa182
Merge "Disable VisualEditor in content namespaces on svwiktionary"