Add a CLI command to view volumes

Related: #707, #706, #691, #447, #613, #637, #622, #461, #674, #579, #465, ...

Many users have reported issues with volumes, and docker likes to silently ignore volumes when the host path doesn't exist.

To help debug these issues, and to help developers better understand the volumes being used by their containers, this PR adds a new cli command `fig volumes`.

It will display a table like this, with all the volumes the containers are using:

```
         Name                 Path         Mode                                             Host                                           
------------------------------------------------------------------------------------------------------------------------------------------
examples_cadvisor_1      /var/lib/docker   rw     /var/lib/docker                                                                          
examples_cadvisor_1      /var/run          rw     /run                                                                                     
examples_cadvisor_1      /sys              ro     /sys                                                                                     
examples_longestname_1   /etc              rw     /var/lib/docker/vfs/dir/531d0515d0fefc1a485e83f933810677d8d6132092387cc1ef8029960585135a 

```