* Pressing enter now always adds whatever was in the input box
to the invite list, if it's a valid address (previously it
added it to the list of it was a search result but submitted
the form straight away if there were no results).
* Remove isValidAddress as it was only used in the context of
testing whether its return value was true or null (where null
meant "unsure") so just use getAddressType instead.
Pasting a list of addresses into the box will now pop up a dialog to confirm and show you the success / failure state of each address. It will also not die if it gets rate limited.
Fixes https://github.com/vector-im/vector-web/issues/1713
