💡 Make collections indexable by names

[demberto]

Currently, model collections like Patterns, ChannelRack, Arrangements, Mixer, Insert and so on implement __getitem__ to allow passing an index of the model.

Example:

project.arrangements[1]    # Arrangement(name="...", ...)

This works, but has little value practically speaking. Nobody remembers the index of the pattern or much less of a channel.
Models have a name property which can be used as a parameter for the __getitem__ method. Once that is done,

project.arrangements["arrangement_name"]    # returns an Arrangement with that name