Make the message TextField expanding, wrapping and scrollable

Summary:
A scrollbar will show if the entered text fills more than 1/3rd
of the screen, pressing enter will send the message and shift +
enter will add a new line.

Reviewers: KDE Connect, sredman

Reviewed By: KDE Connect, sredman

Subscribers: sredman, kdeconnect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D17224