Partition visualizer not accessible to keyboard users

**Describe the bug**

Hey folks, without access to a mouse it's not possible to select a partition using the graph. This is tricky if you have a bluetooth mouse and haven't set it up yet during the install process on a real machine.

This graph:

The workaround is to go to "Try Demo Mode", use search to get to the bluetooth panel, add your mouse, then open "Install Elementary"

**To Reproduce**
Steps to reproduce the behavior:
1. Install beta, go through keyboard options
2. Click on Custom (Advanced)
3. Try to use the keyboard to select your partition

**Expected behavior**
Active states, and pressing enter/space to trigger the popover

**Desktop (please complete the following information):**
- OS: e6 beta
- Browser N/A