Auto merge of #4646 - alexcrichton:progress, r=matklad

Add a number of progress indicators to Cargo

This commit is an attempt to stem the tide of "cargo is stuck updating the
registry" issues by giving a better indication as to what's happening in
long-running steps. The primary addition here is a `Progress` helper module
which prints and manages a progress bar for long-running operations like git
fetches, git checkouts, HTTP downloads, etc.

The second addition here is to print out when we've been stuck in resolve for
some time. We never really have a progress indicator for crate graph resolution
nor do we know when we're done updating sources. Instead we make a naive
assumption that when you've spent 0.5s in the resolution loop itself (not
updating deps) you're probably done updating dependencies and on to acutal
resolution. This will print out `Resolving crate graph...` and help inform that
Cargo is indeed not stuck looking at the registry, but rather it's churning away
in resolution.

**Downloading all Servo's dependencies**

[![asciicast](https://asciinema.org/a/JX9yQZtyFo5ED0Pwg45barBco.png)](https://asciinema.org/a/JX9yQZtyFo5ED0Pwg45barBco)

**Long running resolution**

[![asciicast](https://asciinema.org/a/p7xAkSVeMlkyvgcI6Gx7DZjAV.png)](https://asciinema.org/a/p7xAkSVeMlkyvgcI6Gx7DZjAV)