closes https://github.com/TryGhost/Team/issues/1885
- adds limit check for members to the `PublishOptions` class when it's constructed to set a `publishDisabledError` property if the limit check fails
- if `publishOptions.publishDisabledCheck` is present, all publish options in the publish flow are disabled, the underlying error message is shown, and the continue button is removed to prevent filling in everything only to find at the end of the process that publishing fails
- added handling for a `HostLimitError` error from the API when confirming publishing so the proper underlying message is displayed instead of the confusing "Host limit error, cannot edit post" error
- this is a backup measure for any instances where you're under the max members limit when starting the publish flow but are over the limit when you reach the end of the publish flow
refs https://github.com/TryGhost/Team/issues/1586
- added test helper for enabling/disabling members and helpers for disabling mailgun and newsletters
- added `loginAsRole` helper that alleviates duplication of user+role creation and also handles log-out before log-in so it's easier to mix different role tests within a block that has a default role setup in `beforeEach()`
- cleaned up editor tests that were skipped due to using the old publish flow
- added `Publish flow` acceptance test suite with an initial batch of tests
refs a021553203
- keeps text and logic together, avoids duplication of button code just for changing the running/success text
- added a `buttonTextMap` to keep the high-level text states in one place
- added `publishType` getter for easier switching between states in other getters and to have one place for the logic
- updated `confirmButtonText` getter and added `confirmRunningText` and `confirmSuccessText` getters that read from the button text map so the pattern used for getting text to pass as arguments in the template is consistent
