Add mouse gestures

Add mouse gestures using GtkEventControllerMotion with two functions:
  - Middle click + Move left = Go back
  - Middle click + Move right = Go forward
  - Middle click + Move down = Open a new tab
  - Middle click + Move up + Move down = Reload current tab
  - Middle click + Move down + Move right = Close current tab

Fixes: #430
1 job for master in 8 minutes and 18 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #177324
flatpak

00:08:18