Move 'copy file location after saving' to Save Options page

Summary:
Removed check box for 'copy file location after saving' from General options page and added back to Save options page. Also renamed group box to 'Save Location' and renamed label for default save location to 'Default Save Location' to make the group box title more applicable to the 'copy file location after saving' setting.

BUG: 390793
FIXED-IN: 18.12.0

Before:
{F6191546}

After:
{F6191548}

Reviewers: #spectacle, ngraham

Reviewed By: #spectacle, ngraham

Tags: #spectacle

Differential Revision: https://phabricator.kde.org/D14812