Updated where leader key is set and made var in lv-settings (#474)

- Setting leader-key in the init.lua file. You want to set the leader as
  soon as possible so that it's the same everywhere. With the leader
  being set in the lua/lv-which-key/init.lua it resulted in mappings that
  used `<leader>` in the lua/keymappings.lua mapping the the defualt
  leader-key of `\`
- Added the O.leader_key to the lv-settings.lua file so the leader-key
  can be set there, which seems to make more sense.
- Added handling for when the leader-key is `<Space>`. This could be
  made more robust to include other special keys, but I don't think
  many/any of the other special keys would be used as a leader-key (ie
  <BS>, <CR>, <Tab>, <Esc>, <Up|Down|Right|Left>, etc.)

Co-authored-by: Christian Chiarulli <chris.machine@pm.me>

lua/lv-which-key/init.lua

@@ -43,11 +43,6 @@ local opts = {
     nowait = false -- use `nowait` when creating keymaps
 }
 
--- Set leader
-vim.api.nvim_set_keymap('n', '<Space>', '<NOP>', {noremap = true, silent = true})
-vim.g.mapleader = ' '
-
-
 -- no hl
 vim.api.nvim_set_keymap('n', '<Leader>h', ':let @/=""<CR>', {noremap = true, silent = true})