[Applet] Make 'raise maximum volume' global

Summary:
Remove maximum volume control from configuration.
Remove individual maximum volume.
Add a checkbox in applet to enable raise maximum volume for all devices. (not applications)

Depends on D26271

Test Plan:
Before:
2 options exist to raise maximum volume.
One options controls the default output device(by setting the limit).
And a second one controls individual devices/applications.
After:
A checkbox in the applet will raise the max volume for all devices to 150%.

Reviewers: ngraham, #vdg, #plasma, drosca

Reviewed By: ngraham, #vdg

Subscribers: drosca, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26256