INT-1939 Twitter Search Outbound Gateway

JIRA: https://jira.spring.io/browse/INT-1939

Outbound gateway to allow on-demand variable searches.

Also add the `page-size` attribute to inbound adapters (previously
hard-coded to 20).

Also the inbound adapters now `require` a `TwitterTemplate` because even
search requires authentication.

Polishing - PR Comments

- Bump to spring-social-twitter 1.0.0.RC1
- Remove `requires-reply`
- Polishing
- Add integration test

INT-1939 Doc and Rework

Now supports up to 4 search args (as well as a
SearchParameters).