Disable trimwhitespace and drawwhitespace via their configs (#1446)

Instead of completely disabling them, we now use their internal toggle.

Also moved `drawwhitespace` commands inside the plugin.

---

* Fixed bug where commands would show even when plugin was disbled. Also removed antiquated way of disabling.

* Fixed typos.

* Also moved trimwhitespace out of config, if it already has a default enabled value of false.

* Changed documentation.

* Clarified comments.

data/core/commands/drawwhitespace.lua

@@ -1,16 +0,0 @@
-local command = require "core.command"
-local config = require "core.config"
-
-command.add(nil, {
-  ["draw-whitespace:toggle"]  = function()
-    config.draw_whitespace = not config.draw_whitespace
-  end,
-
-  ["draw-whitespace:disable"] = function()
-    config.draw_whitespace = false
-  end,
-
-  ["draw-whitespace:enable"]  = function()
-    config.draw_whitespace = true
-  end,
-})