Invite user screen is confusing

See the conversation starting here: https://matrix.to/#/!tDRGDwZwQnlkowsjsm:matrix.org/$1522462033557572ksHNN:matrix.org

The invite user to room screen is confusing and buggy.

- For example why can I see the user listed when I search for ```aaronraimist:matrix.or``` but when I finish typing ```aaronraimist:matrix.org``` it disappears.

- When I am searching for a local contact, if I have their first middle and last name in the contact but omit their middle name in the search, nothing comes up.

- You can search local contacts by a name or an email but not a phone number?

- As tonycto said it should infer the @ sign at the beginning if you forget that part.

Start at the invite user to room screen and reproduce the Matrix ID, local-contact name, phone-number, and missing-@ search cases described in the issue. Trace the screen's search entry point and compare behavior for partial and complete input; done means the reported contact searches are consistent and the confusing results no longer occur.

Written by the indexing model from the issue text.