Improving remove_servers command syntax.

You can now use the same targeting syntax as all other tasks.

For example:
- Selection of servers: rake remove_servers servers=1,2,3
- Range of servers: rake remove_servers servers=1..3
- All servers: rake remove_servers servers=all
Saving / loading reports for comparison and fallback purposes.
Highlighting balance changes.
Tracking date & time of current and previous reports.