Add Vimtex for Latex support (#512)

* Add vimtex plugin

Vimtex provides a full integration for latex files, see: https://github.com/lervag/vimtex.
Zathura is used as default pdf viewer as it allows live reloading.

* Provide the <leader>L shortcut for Latex operations.

* Move vimtex into the extra plugins section

Add a short comment above extra plugins to introduce their functionality

* Only define whcihKey mapping for Vimtex if O.extras is true

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

lua/lv-which-key/init.lua

@@ -184,6 +184,17 @@ local mappings = {
     }
 }
 
+if O.extras then
+    mappings["L"] = {
+        name = "+Latex",
+        c = {"<cmd>VimtexCompile<cr>", "Toggle Compilation Mode"},
+        f = {"<cmd>call vimtex#fzf#run()<cr>", "Fzf Find"},
+        i = {"<cmd>VimtexInfo<cr>", "Project Information"},
+        s = {"<cmd>VimtexStop<cr>", "Stop Project Compilation"},
+        t = {"<cmd>VimtexTocToggle<cr>", "Toggle Table Of Content"},
+        v = {"<cmd>VimtexView<cr>", "View PDF"}
+    }
+end
 -- TODO come back and fix visual mappings
 -- local visualOpts = {
 --     mode = "v", -- Visual mode