Rework Sign Ups UI and terminology

[rmccue]

"Sign Ups" is the internal name for this stuff really, it shouldn't be exposed to users. We should move this under the "Users" menu, and consider renaming.

Possible alternative names:

• Pending Invitations
• Unconfirmed Users

We should also consider removing the "Add New" page, or combining it with the existing "Users > Add New" page.

[rmccue]

The way signups works is pretty confusing, and mostly makes sense for a massive multisite install like WordPress.com. Long-term, we might want to look at skipping this process entirely for the sorts of sites that Altis is used for, but in the meantime we can at least clarify the UI.

When you add a user to a multisite instance, you're actually inviting them to join the site. WordPress creates an entry in the signups table to register this invitation, and the invitation is converted to a real user when they accept.

To clarify this flow, we should do the following:

• Remove the "Add New" page under signups, as it duplicates the regular user creation pages
• Rename Signups to "Invitations" everywhere it's used
• On the user creation page, clarify that a user invitation will be sent, and will be visible in the invitations page (this is linked to the "send email to user" checkbox, which is unclear currently)

This may require changes to the upstream signups plugin we're using to implement this functionality currently.

As a stretch goal, we should look at whether we can redesign the user creation screen in a similar way to #93 to be much clearer about what actions will take place and which action a user should perform.

[rmccue]

(Also, it may be worth considering copying some of the changes I made to the Altis Central auth signup process. Ping me in Slack for more details.)

[jazzsequence]

I got as far as I could on this trying to just use existing WordPress hooks to move and rename the Sign ups page into the Users menu in #187. It needs more work but it's a start.