Run the membership reducer even for incognito.
The GUI needs to differentiate between 'unfetched' (`undefined`) and 'no membership' (`''`), so we must call the action/reducer for the incognito case as well.
## Ticket
1572
Always check for availability before use.
## Changes
- Consolidated the keys into one place for easier tracking.
- It'll also be easier to code using constant autocomplete.
- Cleaned up the wrapper to be as close as the original.
- Updated existing code to use the wrapper (even if they already handled the availability) to encourage future code to just use the wrapper.
- Corrected flow definitions.
- Properly differentiate between "not yet fetched" and "no membership" as "undefined" and "<empty string>", respectively. There are GUI elements that need to know the unfetched case.
## Issue
Closes 385
## Approach
As mentioned in the ticket, the current places where that info is needed is in the Invites Page and Social Share Component.
1. Invites Page: it is already doing the fetch on mount, so no issue there.
2. Social Share: show spinner until the data is fetched.
- "The publisher has chosen to" -- Fix incomplete string, probably broken by linter.
- Fix hardcoded email in invite snackbar.
- Fix 'Upload Settings' to new lower-case style.
- Add few more missing ones.
- Consolidated "Claim xxx" strings together.
- Removed duplicate "Confirming..." due to branch merging.
