Add Java installation instructions to INSTALL.OSX.rst

[ci skip]
Add a package.json for managing frontend dependencies

This allows us to install all but compass locally in the project rather
than relying on global executables.
Install frontend dependencies in bootstrap
Update webassets paths in configuration files

These now use project local dependencies rather than relying on them
being installed on the users PATH.
Update INSTALL docs to instruct on node installation

This reduces the number of installation steps for most platforms. Node
installation instructions taken from the Joyent wiki[1].

[1]: https://github.com/joyent/node/wiki/Installing-Node.js-via-package-manager
Merge pull request #1271 from hypothesis/node-modules

Manage frontend dependencies with npm
Merge pull request #1270 from hypothesis/osx-install-java

Add Java installation instructions to INSTALL.OSX.rst
Pin repoze.sendmail until upstream fixes known bug

repoze/repoze.sendmail#31
Add .buildpacks for heroku-buildpack-multi
Remove webassets node binary paths in production

Our common production deployment assumes a heroku or heroku-like
environment. In this environment, the PATH is already set from the
buildpack.
node deps are not development only

Until we start packaging and releasing a version with pre-built
assets, these are needed at runtime.
Add node engines to package.json
Remove obsolete test hacks
Fix failing annotator login test on OSX

The SERVER_NAME environment variable on OSX defaults to 127.0.0.1 where
on other systems it's localhost. When a user is created the provider
defaults to the request.server_name value, this caused the assertion
to fail.

Ideally we'd be able to set the SERVER_NAME in the config for all
platforms, but I was unable to find the correct config value for this.
So in the mean time I'm just accepting both options as valid.