Allow referencing servers via nicknames

[Aptimex]

(Pending the merge of #48 )

Allow replacing some args like --server-address with a server's nickname and have it deduce the correct API address from that.

Could either introduce a separate arg like --nickname, or (probably easier) just have existing args additionally check if the passed value is a valid nickname that can be used to deduce the correct value.

Also need to figure out how to handle duplicate nicknames since currently those don't have to be unique. Possible solutions:

• Prevent duplicates directly in the configure and add commands; seems messy
• Let it just pick the first match it finds and note that the selection behavior is undefined if duplicates exist
• Throw an error if duplicates exist; this is probably the best combo of simple but robust