Disable Kramdown warnings

Since we enabled kramdown in !108 (merged), when developing locally, we see a lot of warnings like the following:

kramdown warning(s) for                                                                                   
  No link definition for link ID 'starter' found on line 165
  No link definition for link ID 'ultimate' found on line 169
  No link definition for link ID 'ultimate' found on line 171
  No link definition for link ID 'ultimate' found on line 173
  No link definition for link ID 'premium' found on line 184
  No link definition for link ID 'premium' found on line 291
  No link definition for link ID 'premium' found on line 292
kramdown warning(s) for                                                                                               
  Found block HTML tag 'ul' in span-level text on line 683
  Found block HTML tag 'li' in span-level text on line 683
  Found invalidly used HTML closing tag for 'li' on line 683
  Found block HTML tag 'li' in span-level text on line 683
  Found invalidly used HTML closing tag for 'li' on line 683
  Found invalidly used HTML closing tag for 'ul' on line 683
  No link definition for link ID 'starter' found on line 64
  No link definition for link ID 'ultimate' found on line 65
  No link definition for link ID 'ultimate' found on line 66
  No link definition for link ID 'ultimate' found on line 67
  No link definition for link ID 'ultimate' found on line 70
  No link definition for link ID 'premium' found on line 72
  No link definition for link ID 'premium' found on line 159
  No link definition for link ID 'starter' found on line 312
  No link definition for link ID 'ultimate' found on line 323
  No link definition for link ID 'ultimate' found on line 339
  No link definition for link ID 'ultimate' found on line 355
  No link definition for link ID 'ultimate' found on line 416
  No link definition for link ID 'premium' found on line 432
  Found block HTML tag 'ul' in span-level text on line 1
  Found block HTML tag 'li' in span-level text on line 1
  Found invalidly used HTML closing tag for 'li' on line 1
  Found block HTML tag 'li' in span-level text on line 1
  Found invalidly used HTML closing tag for 'li' on line 1
  Found invalidly used HTML closing tag for 'ul' on line 1
  No link definition for link ID 'premium' found on line 748

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Let's disable them until we find a way to maybe fix them. They don't provide any useful information for now and they clutter our screens.