Add option to abaco executions to list the most recent execution

[bbartley]

For example, using a -l switch to get the last execution:

$ abaco executions -l <my_actor_alias>
P0BNvJo1M4xyl  COMPLETE

In practice, I typically only care about the most recent execution. In addition, I am using shell scripts that parse the most recent execution from an ever-growing list of executions, which might not be sustainable in the long term.

[bbartley]

Similarly, it would be helpful to have an option for printing the log of the most recent execution, without having to specify the execution hash. For example:

$ abaco logs -l <my_actor_alias>

This would make debugging a lot more efficient. Currently I have to print out a list of executions, copy the hash of the most recent one, and then paste that into my subsequent logs command, which can be a bit of a hassle.