The dialog form has a simple text input for the sender's name.
This can lead to typos or mistakes if the GM wants to send a message
using the same sender name as a previous message.
Add a new function that goes through all the players' histories and
compiles a list of all unique senders, which we can then use to build
a list of hints that will be used to show suggestions when the GM fills
the sender name in the form.
This is currently quite ineficcient as it re-does all the work for every
single dialog.
A better way would be to cache it or store it explicitly somewhere when
we send a message, but this would require a way for the GM to edit it.
Move some generic constants and functions, or supporting functions
to a new file.
This makes the main script smaller and makes it more focused on the
core functionality of the module.
