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/shared/misc/.config/nvim/init.vim

@@ -267,7 +267,7 @@ nnoremap <leader>ea :vsplit ~/aliases.zsh<CR>
 nnoremap <leader>ef :vsplit ~/functions.zsh<CR>
 nnoremap <leader>el :vsplit ~/variables.zsh<CR>
 nnoremap <leader>ex :vsplit ~/.Xresources<CR>
-nnoremap <leader>ei :vsplit ~/.config/i3/config<CR>
+nnoremap <leader>ei :vsplit ~/.config/i3/config.shared<CR>
 
 " quickly source your vimrc
 nnoremap <leader>sv :source $MYVIMRC<CR>