Don't show links for disabled link types

Parsed and manual links will show up in a block when they are disabled. This shouldn't happen.

Links of these two types are determined on node edit, not whevever the block is displayed. This makes sense because if the types are disabled and then enabled, no data is lost. However, when the related links block is being displayed, a check should be put in place to make sure that links of whatever type are actually enabled.

I suppose this could be fixed in 4.7 as well.