Do not print todo numbers of activated todos.

After performing this command, the CLI will archive the completed
todos. This may cause the numbers to shift, invalidating the todo
numbers that DoCommand just printed before.
Complete the test case.
Make a GrepFilter for every argument passed to the ListCommand.

This ANDs all arguments, resulting in the todos that match all
substrings.
Add possibility to specify which value to replace.
Call remove_tag with the current value, if available.
Add 'tag' subcommand.