closes#1910
- Installs Dart SDK
- Installs ng2/dart sources from the pub package site.
- Re-enables doc build on Travis
- install Dartium browser for eventual testing.
- allow TMP and PKG to be set by developer before calling, e.g., install-dart-sdk.sh.
- removes `npm install -g gulp --no-optional` has been removed since it does not appear to be needed.
- Implements most of #1907.
closes#1900
This single install script:
- Checks for the proper version of node (some of us develop with node
v4 on other sites, and it is too easy to forget to switch to v5 for
angular.io).
- Applies the patch (that is necessary to support harp compilation of
Dart API pages).
