Disables filepicker on old Chrome versions

Displays an error dialog if the user tries to mount a local directory, when the version of Chrome does not support this operation.
Factors out version checking into a function
Changing to use versioned kernels.
Fixing typo.
Update README.md
Override platform in kernel.py.
Don’t use 8888 as default port

caching redirects cause problems with other apps (IPython)
on the same ports.
update version to 8 in manifest
Merge pull request #63 from MatthewTurk/master

Drop zeropy from names, move to versioned, and fix platform
Merge pull request #64 from minrk/not-8888

Don’t use 8888 as default port
Merge pull request #59 from jupyter/filepicker

Disables filepicker on old Chrome versions
Fix typo: verison->version
Merge pull request #65 from mr-c/patch-1

README.md: verison->version
Updates binary version and manifest version

Updates binary version to use newest PNaCl build, and updates manifest version.
Merge pull request #68 from jupyter/update

Updates binary version and manifest version
Change min chrome version

Earlier min chrome version was based on current stable mac build, but other platforms use earlier versions.
Merge pull request #69 from jupyter/update

Change min chrome version
Adds colabtools stage to install_chrome.py

Adds back the stage of adding the colabtools library to the .tar.gz file, to the installation procedure.  This was removed when converting to the python based installation.
Removing comments object.
Cleaning up the interface and making it more like IPython.