assert minimum version of npm required to get web staff client deps

[Galen Charlton]

It has been observed that on a Debian Wheezy system that's been around long enough to still have npm 1.4.9 installed, running "npm install" to fetch the web staff client's dependencies fails to bring in angular-sanitize.

https://docs.npmjs.com/files/package.json suggests that we could make two changes to avoid this issue (and potential future issues):

- add to package.json an "engine" declaration that asserts the minimum version of npm required. (We know that 3.10.10 works and that 1.4.9 does not)
- passing '--engine-strict true' to the npm command, particularly when it's invoked by make_release.

Evergreen 3.0+

[Jason Stephenson (jstephenson)]

I've also had Node.JS suggest that I upgrade npm. After doing that recently, my build was broken. I do not recall the version number off the top of my head, but should be able to get it if necessary. We may want to assert maximum version numbers as well.

Now that we no longer support Debian Wheezy as an install target, the minimum version may be less of an issue.