Notebook, File and Terminal Favicons are low resolution

On high-res screens (such as a Retina Macbook Pro's), some of the favicons are blurry.
The [main favicon](https://github.com/jupyter/notebook/blob/master/notebook/static/favicon.ico) is good:

This is 64x64 px, which displays nicely.

However, the other favicons ([notebook](https://github.com/jupyter/notebook/blob/master/notebook/static/base/images/favicon-notebook.ico), [terminal](https://github.com/jupyter/notebook/blob/master/notebook/static/base/images/favicon-terminal.ico), [file](https://github.com/jupyter/notebook/blob/master/notebook/static/base/images/favicon-file.ico) and hourglass icons) are lower resolution, at only 16x16 px:

Should higher resolutions versions be included, so they are less blurry on pixel-dense screens?

Inspect the favicon assets in notebook/static/base/images/, especially favicon-notebook.ico, favicon-terminal.ico, favicon-file.ico, and the hourglass icons, and compare them with notebook/static/favicon.ico. Check the icons on a high-DPI display or browser scaling, then provide higher-resolution versions for the blurry assets so they render sharply.

Written by the indexing model from the issue text.