Do correct settings check on total email limit toggle

Due to some inconsistency in the way settings are saved, the toggle for
limiting the total number of email invitations can be stored as a null value
or as 'no'. This changeset makes the runtime check more forgiving.
Readme update
Adds Danish translation
Bumps version numbers to 1.0.16
Be more intelligent about where the Invite Anyone menu is hooked
By Email form improvements

- Adds a notice about maximum invited people
- Normalizes the way description text is presented

Props humanshell
Bumps version numbers to 1.0.17
Adds pt_BR translation
Updates ru_RU
Updates readme
Adds filters to control whether friend/follow requests are send on invitation acceptance
Readme update
Bumps version numbers to 1.0.18
When pulling up list of site members on group invites, don't fetch WP_User

This was causing memory timeouts on very large installations
Readme update
Fixes prepare() warnings
Updates readme
Bumps version numbers to 1.0.19
Updating italian translation
Readme