In gradle build, properly do npm install for client

[n8kim1]

In gradle builds: if new packages are introduced in the visualizer, we can sometimes fail to install them, and so things fail to run/build.

To install npm packages for the client: you need to run npm install-all in the top level directory, as stated by the client readme and package.json. This cd's into each of the two big subfolders, and properly does install. (otoh, npm install performs default behavior -- it tries to install everything in the wrapper that is the top directory, which is not quite what we want here)

Unforunately, in https://github.com/battlecode/battlecode21/blob/master/build.gradle#L243 --
commandLine 'npm', 'install'
This should really be install-all