Fix rendering issues causing [object Object] to appear in search

This request fixes #338 by doing a deep traversal over objects when highlighting the selected parts of the text. It also adds highlighting capability for a few more elements (in addition to the previous p elements).

The issue was previously addressed in another merge request, which caused other rendering errors in different contexts. I believe those issues were caused by incorrect filtering conditions in the deep traversal, and the new changes must have fixed them as well.