Feature: Change markdown engine to markdown it

This commit removes the old evilstreak markdownjs engine.

- Adds specs to WhiteLister and changes it to stop using globals
    (Fixes large memory leak)
- Fixes edge cases around bbcode handling
- Removes mdtest which is no longer valid (to be replaced with
    CommonMark)
- Updates MiniRacer to correct minor unmanaged memory leak
- Fixes plugin specs

script/import_scripts/lithium.rb

@@ -53,7 +53,6 @@ class ImportScripts::Lithium < ImportScripts::Base
 
   def execute
 
-    SiteSetting.allow_html_tables = true
     @max_start_id = Post.maximum(:id)
 
     import_categories