Update left panel labels and subtab look

In the left panel, introduce the following changes:

Change label of the "SEARCH" subtab "GENERIC" to "CONTENT"
In the "SEARCH" subtab "GENERIC" change label above the search bar from "SEARCH:" to "SEARCH IN CONTENT:"

Change the look of the "SEARCH" subtab "GENERIC" - remove the line separator between the "SEARCH" tab and the subtab, see image. It makes the "GENERIC" search subtab separate from the "SEARCH" tab above.