Add new encryption cipher for Android 2.3 (API 9+) support

Summary:
Arch linux recently updated libraries which dropped support for RC4, used for connections to Android before Android 3 Honeycomb. Other distributions may also be affected (or will be affected in the future).

This adds a new cipher, supported by Android API 9+.

Test Plan: With this change (and corresponding desktop change) the app can connect again.

Reviewers: KDE Connect, albertvaka

Reviewed By: KDE Connect, albertvaka

Differential Revision: https://phabricator.kde.org/D9449