Use more contextual strings for some button labels

Summary:
Every Bluetooth error's "fix this error" button's text is "Fix it". However, some issues are not actually problems per se from the user's perspective, so the text can imply the existence of a problem where none exists.

In the case where the Bluetooth adapter is powered off or disabled, display a more contextually appropriate string instead ("Turn On" and "Enable", respectively)

CCBUG: 394778
FIXED-IN: 5.14

Test Plan:

Reviewers: Plasma, VDG, drosca

Reviewed By: drosca

Subscribers: broulik, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D13346