INT-3339: Add `priority` to the `JdbcChannelMS`

JIRA: https://jira.spring.io/browse/INT-3339

INT-3339: Improve `priority` logic

INT-3339: Add `MESSAGE_SEQUENCE` stuff

INT-3339: Docs

INT-3339: Polishing and PR comments

INT-3339 Polishing

Fix Oracle Test Case.
Doc polishing.
INT-3366 Increase Script Test Timeouts

JIRA: https://jira.spring.io/browse/INT-3366

Timings are too tight for Travis.

Also fix a JDK8 javadoc problem.
INT-3338: MongoMS: add `priority` and `sequence`

JIRA: https://jira.spring.io/browse/INT-3338
INT-3338: Add Docs
INT-3338: Make `priority` 'smart'

Add `Sort` for all group queries dependently of `priorityEnabled`.
It allow do not configure separate collections for different type of `MessageStore`
INT-3338: Add `MongoDbChannelMessageStore`
INT-3338: Polishing, Fixes, Improvements