This commit introduces a couple of changes:
1. When editing a chat channel's slug, we were using `this.model.set("title", title)` when the `set`
function does not exist. This was actually throwing the error in the
"can edit slug" system test where the modal was not closed after
saving and was flashing an error.
2. Introduce `PageObjects::Pages::ChatChannelAbout` and
`PageObjects::Modals::ChatChannelEdit` page object to encapsulate
logic better.
This commit allows us to set the channel slug when creating new chat
channels. As well as this, it introduces a new `SlugsController` which can
generate a slug using `Slug.for` and a name string for input. We call this
after the user finishes typing the channel name (debounced) and fill in
the autogenerated slug in the background, and update the slug input
placeholder.
This autogenerated slug is used by default, but if the user writes anything
else in the input it will be used instead.
Alan Guo Xiang Tan
Martin Brennan