Improve wording of split view/pane settings

Summary:
I found these strings very hard to understand then translate without looking into the code because the use of "view" refers to both "the split view" and "the left pane and the right pane of the split view".

This patch attempts to explicitly mention panes when needed.

Reviewers: #dolphin, angeloevertonjr, ngraham

Reviewed By: #dolphin, ngraham

Subscribers: ngraham, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D19579