Support shared, device-specific i3 configurations

Separated i3/configuration since some of my devices support XFree86 keysyms
while others do not. This introduced some cascading changes.

- Removed ~/.config/i3/config from this repo. Since I will be switching between
  devices semi-regularly and that file will be generated each time I switch to a
  different device running an X session, I don't want the i3/config to spam my
  `gst` and `gd` when I haven't changed configuration in either config.shared or
  config.device.
- Update aliases, variables, etc. to point to config.shared instead of the
  generated file.
- Ensure that X sessions generate the i3/config file.
- Ensure that i3 reload and restart command generate the i3/config file.

configs/laptop/misc/.config/i3/config.device

@@ -0,0 +1,18 @@
+# Laptop-specific configuration
+
+# My laptop has keys for XFree86 signals that my desktop keyboard currently
+# doesn't have.
+
+# volume controls
+bindsym XF86AudioRaiseVolume exec --no-startup-id pactl set-sink-volume @DEFAULT_SINK@ +10%   # MBP Volume Up
+bindsym XF86AudioLowerVolume exec --no-startup-id pactl set-sink-volume @DEFAULT_SINK@ -10%   # MBP Volume Down
+bindsym XF86AudioMute        exec --no-startup-id pactl set-sink-mute   @DEFAULT_SINK@ toggle # MBP Mute
+
+# playback controls
+bindsym XF86AudioPrev exec --no-startup-id playerctl previous
+bindsym XF86AudioPlay exec --no-startup-id playerctl play-pause
+bindsym XF86AudioNext exec --no-startup-id playerctl next
+
+# screen brightness controls
+bindsym XF86MonBrightnessUp   exec light -A 10
+bindsym XF86MonBrightnessDown exec light -U 10