Simplify whitespace handling in build/ Jinja templates

No change to generated code, just cleanup.

This adds the flags:
lstrip_blocks=True
trim_blocks=True
...to the Jinja environment setup

This means we don't need {%- everywhere, and also allows us to indent control blocks.

(Other than that, a few consistency fixes of {{ foo() }} => {{foo()}} and " => ')

This CL does not change generated code, to simplify testing and review.
This turned up lots of minor whitespace errors or warts, which I've marked
with FIXME and will fix in a followup.

R=abarth

Review URL: https://codereview.chromium.org/236673002

git-svn-id: svn://svn.chromium.org/blink/trunk@171422 bbb929c8-8fbe-4397-9dbb-9b2b20218538