bower install of elements freezes server

[jhpedemonte]

Noticed yesterday when downloading threejs (which takes a while) that the bower install of elements completely freezes the server, such that I can't load or work on a different notebook. If possible, bower install should be handled asynchronously so as not to bog down everything else.

[parente]

The subprocess call here:

https://github.com/jupyter-incubator/declarativewidgets/blob/master/nb-extension/python/urth/widgets/urth_import.py#L26

can be made asynchronous with:

http://tornado.readthedocs.org/en/latest/process.htmlhighlight=subprocess#tornado.process.Subprocess

The issue then is how to design the flow of execution between the backend installing elements and the frontend trying to use them so that issue #25 is not made worse by the asynchronous call.

[zackmorris]

I'm looking into switching the subprocess call to use Tornado's subprocess function.

[parente]

Be aware that this fix is going to further break #25 which probably needs to be fixed first or in parallel.

[zackmorris]

#61 has the aforementioned changes to the subprocess call.

We're going to need add a queue for tracking the state of each package's installation progress. This will prevent overlapping dependencies by maintaining a sequential installation of packages based off of the order they were sent to the server.

[lbustelo]

We are going to put this on hold for now to first figure out the best way to reliably have Run All work.