Route policy declarations (for network routes only for now).

Allows packages such as stream and accounts to declare URL prefixes
such as /sockjs/ and /_oauth/ to be network routes.

Updates server to avoid serving app HTML on network routes.

Checks for conflict between files in public/ and network routes.  For
example, the developer might not know that /sockjs/ is reserved, and
might create a file "public/sockjs/socks-are-great.png".
Regexps that match "undefined" should not match nonexistent fields.
Merge remote-tracking branch 'remotes/origin/pr/679' into devel. Fixes #679.
Fix override for icon-white

CSS Selector was not matching => wrong image loaded in certain cases
Switch to using the right URI and comment what we are doing
Fix css selector for white icons in bootstrap

Merge branch 'pr-683' into devel
Merge branch 'devel' into ddp-pre1