Bugfixes, improved npm/yarn install flow

New behavior of npm_install and yarn_install rules:

• instead of symlinking the package.json file into bazel, we now copy it. This means Bazel will no longer make edits to your lock file.
• the output from the command will be streamed to your terminal. Instead of bazel silently saying "analyzing" you'll now see the install progress. Set quiet to True in the npm_install or yarn_install rule to get the previous behavior
• the exclude_packages attribute filters out @bazel/bazel from being installed again under Bazel.
• we no longer omit test and .bin directories from the generated BUILD file
• set the --network-timeout option when running yarn install since we saw a lot of timeouts