Re-implement Meta-E global launch shortcut using KGlobalAccel

Summary:
FEATURE: 405302
FIXED-IN: 19.08.0

Test Plan:
1. Apply patch
2. Reboot (didn't work until I rebooted or logged out and back in again)
3. Hit {key Meta E}
4. Dolphin Launches

Reviewers: #dolphin, elvisangelaccio, davidedmundson

Reviewed By: #dolphin, elvisangelaccio

Subscribers: kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D20229