Change icons to more appropriate versions

Summary:
This change changes the media-skip icons to go- icons, more suitable paging back and forth through images.
This also adds First and Last icons, as well as an icon for the save dialog when closing the application.

Main Menu Before:

Main Menu After:

Save Dialog Before:

Save Dialog After:

Test Plan: Page back and forth with the navigation buttons. Make changes to images, attempt to close the application to trigger the save dialog, and attempt discarding changes.

Reviewers: Gwenview, ngraham, rkflx

Reviewed By: Gwenview, ngraham, rkflx

Subscribers: rkflx, ngraham

Tags: Gwenview

Differential Revision: https://phabricator.kde.org/D10847