Add eb list-solution-stack command

Fix #8.

Output is like this:

```
$ ebfly eb list-solution-stacks

=== Docker ===
64bit Amazon Linux 2014.03 v1.0.0 running Docker 1.0.0
64bit Amazon Linux 2014.03 v1.0.1 running Docker 1.0.0
64bit Amazon Linux 2014.03 v1.0.2 running Docker 0.9.0
64bit Amazon Linux 2014.03 v1.0.5 running Docker 0.9.0

=== Node.js ===
32bit Amazon Linux 2014.03 v1.0.3 running Node.js
64bit Amazon Linux 2014.03 v1.0.3 running Node.js
64bit Amazon Linux 2014.03 v1.0.4 running Node.js

=== PHP ===
32bit Amazon Linux 2014.03 v1.0.3 running PHP 5.4
32bit Amazon Linux 2014.03 v1.0.3 running PHP 5.5
32bit Amazon Linux running PHP 5.3
64bit Amazon Linux 2014.03 v1.0.3 running PHP 5.4
64bit Amazon Linux 2014.03 v1.0.3 running PHP 5.5
64bit Amazon Linux 2014.03 v1.0.4 running PHP 5.4
64bit Amazon Linux 2014.03 v1.0.4 running PHP 5.5
64bit Amazon Linux running PHP 5.3

=== Python ===
32bit Amazon Linux 2014.03 v1.0.3 running Python
32bit Amazon Linux 2014.03 v1.0.3 running Python 2.7
32bit Amazon Linux running Python
64bit Amazon Linux 2014.03 v1.0.3 running Python
64bit Amazon Linux 2014.03 v1.0.3 running Python 2.7
64bit Amazon Linux 2014.03 v1.0.4 running Python
64bit Amazon Linux 2014.03 v1.0.4 running Python 2.7
64bit Amazon Linux running Python

=== Ruby ===
32bit Amazon Linux 2013.09 running Ruby 1.9.3
32bit Amazon Linux 2014.02 v1.0.1 running Ruby 1.8.7
32bit Amazon Linux 2014.03 v1.0.2 running Ruby 1.9.3
32bit Amazon Linux 2014.03 v1.0.3 running Ruby 1.9.3
32bit Amazon Linux running Ruby 1.8.7
32bit Amazon Linux running Ruby 1.9.3
64bit Amazon Linux 2013.09 running Ruby 1.9.3
64bit Amazon Linux 2014.02 v1.0.1 running Ruby 1.8.7
64bit Amazon Linux 2014.03 v1.0.2 running Ruby 1.9.3
64bit Amazon Linux 2014.03 v1.0.2 running Ruby 2.0 (Passenger Standalone)
64bit Amazon Linux 2014.03 v1.0.3 running Ruby 1.9.3
64bit Amazon Linux 2014.03 v1.0.3 running Ruby 2.0 (Passenger Standalone)
64bit Amazon Linux 2014.03 v1.0.3 running Ruby 2.0 (Puma)
64bit Amazon Linux 2014.03 v1.0.4 running Ruby 1.9.3
64bit Amazon Linux 2014.03 v1.0.4 running Ruby 2.0 (Passenger Standalone)
64bit Amazon Linux 2014.03 v1.0.4 running Ruby 2.0 (Puma)
64bit Amazon Linux 2014.03 v1.0.5 running Ruby 2.0 (Puma)
64bit Amazon Linux running Ruby 1.8.7
64bit Amazon Linux running Ruby 1.9.3
```