fix($sanitize): sanitize DOCTYPE declarations correctly

HTML to be sanitized that contains a DOCTYPE declaration were causing
the HTML parser to throw an error.  Now the parser correctly removes
the declarations when sanitizing HTML.

Closes #3931
docs(select): clarify usage

The wording seemed confusing and these adjustments seem to capture the intent
with less turbulence.

Closes #4257
docs(tutorial): update examples to show best practices

Closes #4256, #4255, #4254, #4253, #4250, #4092
docs(tutorial): improve wording and consistency
refactor($animate): avoid checking for transition/animation support during each animation
fix($animator): ensure elapsedTime always considers delay values
refactor($animator): queue all successive animations to use only one reflow
fix(ngAnimate): disable all inner animations for child nodes even if no animations are present