Gave plasmoid some love

Summary:
Make the plasmoid content transparent
Include battery info in header
Only show remotekeyboard input if available
Make header always centered

before:

after:

Reviewers: KDE Connect, apol

Reviewed By: KDE Connect, apol

Subscribers: jeanv, albertvaka, apol, KDE Connect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D6943