docs(404 errors): provide a better 404 experience

It is a bit rough and ready but does a better job than nothing.
style(jsdoc tags): remove/ammend invalid tags

As highlighted by the new sterner dgeni.
docs(guide/directive): fix typo

`restictions` -> `restrictions`

Closes #6604
docs(guide/migration): fix typos

A few typos fixed.

Closes #6605
docs(guide/migration): fix broken link
docs(ngBind): fix typo

`preferrable` -> `preferable`

Typo fixed

Closes #6606
chore(build): upgrade grunt-jscs-checker to ~0.4.0

this is primarily to resolve peerdependency version mismatch issue
docs($sce): correct typo

`consititute` -> `constitute`

Typo fixed

Closes #6607
docs(changelog): release notes for 1.3.0-beta.1 retractable-eyebrow
chore(release): Update package.json to reflect 1.3.x version
chore(release): update cdn version
docs(Error404): improve search results layout
docs(Error404): better heading