Enable neovim through home-manager

- We need to set the default editor to just "nvim" not a particular path, as
  this allows us to override nvim in our home
- Add the mapleader bind to the start of init.vim
- As the leader is interpreted whenever we make a keybind, we must have it at
  the start or it won't be respected for some of our keybinds (but will be for
  others)
- Package the scrollbar plugin and install it
- Setup configs for stuff like treesitter, theme, COC, scrollbar etc.
- Add git capabilities to neovim
- Install fugitive, gitgutter and git-conflict, along with some other basic git
  stuff
- Allow mouse control in neovim
diff --git a/modules/neovim/airline/theme.vim b/modules/neovim/airline/theme.vim
new file mode 100644
index 0000000..29cd139
--- /dev/null
+++ b/modules/neovim/airline/theme.vim
@@ -0,0 +1,3 @@
+let g:airline_theme = "onehalf"
+let g:airline_highlighting_cache = 1
+let g:airline_powerline_fonts = 1