Support multi-monitor setups

First run of Falkon after booting, with dual displays, I could not move the window from the primary display (on the right) to the required display (on the left).

**To Reproduce**
Steps to reproduce the behavior:
1. Boot
2. click the dock icon for the browser

**Expected behavior**
A clear and concise description of what you expected to happen.

3. the window should be draggable, movable.

**Screenshots**


**Version (please complete the following information):**
- live
- hello-0.5.0_0E223-FreeBSD-12.2-amd64.iso

**Computer (please complete the following information):**
- HP EliteBook 8570p
- physical.