CLI messages improvements.

Improvements to the CLI:
- Removed big Harp banner with a much simpler message.
- Added message that shows how to get more information from each command.
- Added usage messages for each command.
- Removed `*` command

Here's what `harp server` looks like:
![image](https://f.cloud.github.com/assets/437440/1784797/9cc54cee-68d8-11e3-93ba-d20cbdf704fd.png)

And here's what `harp multihost` looks like:
![image](https://f.cloud.github.com/assets/437440/1784799/abca4028-68d8-11e3-9dd8-8f4d40beed98.png)