Build cleanup

[blink1073]

Fixes #5017

• Do not cache during uglify on Windows to avoid creating long paths
• Use dev_mode by default when building (but ship prod mode files)
• Run the test builds directly, since a failing TS build does not stop the build, cf bail option does not exit the process codymikol/karma-webpack#66. Fixes the errors that running the builds directly exposed.
• Display the version and app directory when building

[blink1073]

CI is being really mean today:

error Couldn't find package "@phosphor/algorithm@^1.1.2" required by "@jupyterlab/apputils@^0.17.2" on the "npm" registry.

(oh rly?: https://www.npmjs.com/package/@phosphor/algorithm. Ugh...)

[blink1073]

Pip installs are also failing randomly:

+pip install -q -e '.[test]'
Command "/home/travis/virtualenv/python2.7.14/bin/python -c "import setuptools, tokenize;__file__='/home/travis/build/jupyterlab/jupyterlab/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" develop --no-deps" failed with error code 1 in /home/travis/build/jupyterlab/jupyterlab/

[ian-r-rose]

Hm, needs a rebase?

[blink1073]

Rebased.

[ian-r-rose]

Thanks!