Page Grid keyboard shortcut (#) not working with non-us keyboard.

Migrated from https://bugs.launchpad.net/inkscape/+bug/1777294

Steps to reproduce:

• press # (SHIFT-3) to toggle Page Grid visibility

What happened?

• nothing

What should have happened?

• Page Grid should toggled on/off

Inkscape Version and Operating System:

• Inkscape Version: Inkscape 0.92.3 (2405546, 2018-03-11), 0.92.4
• Operating System: Windows
• Operating System version: 10

Additional Notes:

I (greytomorrow) tested against v0.92.4 (macOS and Ubuntu), 1.0beta2 (macOS) and 1.1-dev (Ubuntu). Only the Mac replicated but I believe because of a non-US keyboard layout with # mapped to Alt-à and the Mac doesn't support Alt Gr like Windows and Linux do.