Historically, we've auto-generated package.json in Djblets in order to

have some handy variables that could be used for extension building, to

help keep versions of dependencies manageable by declaring them in

djblets/dependencies.py.
As we've evolved our JavaScript ecosystem, this has become more tedious

to maintain. We have to make changes to the generated package.json and

then mirror them back to dependencies.py. The package.json file was

an ignored file, and we had to be careful with its contents.
This change reverses the role. Now, djblets/package.json is where all

of our NPM dependencies live, and we have a symlink within the top of

the tree to there. Whenever we perform a npm install --save ... (and,

notably, the result of that modifies node_modules), NPM will run a new

script to edit dependencies.py and move those dependencies there.
This way, it should be easier to ensure that we have the right

dependencies in the tree for building static media, looking up types, or

linting the files.
There is a trade-off in that we no longer have the newly-introduced

environment variables for specifying the location of in-development

versions of our Beanbag node.js modules. These made it easier to specify

the path to a package and install it.
The workaround for that is to use npm install --no-save <path> when we

want to test a local version, or use the npm link functionality. It's

not ideal, but the benefits outweigh the downsides.
Our package.json now bundles the latest versions of Backbone, jQuery,

jQuery-UI, and typing modules. These will be installed in node_modules

when building the package, when building extensions, or when consuming

Djblets and using the embedded dependencies. This allows typing and

setting things up to let consumers easily bundle compatible versions of

these packages out of node_modules if desired.

Tested installing and uninstalling dependencies (modifying package.json

in the process) and verifying the updates to dependencies.py.
Verified that the dependencies installed with an empty node_modules

using setup.py develop.