Clean up Draft

[mmccool]

• Add numbered section for intro
• Fix broken references
• Migrate to "respec-w3c" profile.

See also issue https://github.com/w3c/wot-security-best-practices/issues/11, which should however be handled in a separate PR.

[mmccool]

fixed broken refs, but still two ReSpec issues (technically warnings):

• "respec-w3c-common" profile has been deprecated in favor of the "respec-w3c" profile and will not receive any future updates, including the support for W3C 2020 process. Please migrate to "respec-w3c" profile.
• Document uses RFC2119 keywords but lacks a conformance section. Please add a
  .

The second one is noted in https://github.com/w3c/wot-security-best-practices/issues/11 which should be handled in a separate PR. The first one may need some structural changes to the document, but we may as well do it in this PR, too, so I have added it to the todo list.

[mmccool]

Changed respec-w3c-common to respec-w3c, now have a new warning that needs to be resolved:

• Configuration options wg, wgURI, wgId, wgPatentURI, and wgPatentPolicy are deprecated. Please use the group configuration option instead. (Plugin: "w3c/group").