Touch up various user-visible strings

Touch up various user-visible strings

This improves consistency among wording. More clarity is achieved
by avoiding technical terms or terms with multiple meanings.

Notable changes:
-Specify full settings path: "Configure Dolphin > View > General"
in Show Hidden Files whatsThis
-Mention setting to hide files with application/x-trash MIME type
in "Show Hidden Files" whatsThis
-Mention Split View mode in "Copy/Move to Other View" whatsThis
-Reword "Activate Tab" actions to "Go to Tab" (Next, Previous,
Last, numbers)
-Add "Last Tab" iconText, consistent with "Next Tab" & "Previous
Tab"
-Update Split View whatsthis to explain how to tell which view is
"in focus" visually
-Replace "pane" with "view" in split view settings text, and
clarify tooltip text
-Reword "objects" to "items" in whatsThis texts
-Reword "find bar" to "search bar" in Search button whatsThis text