Improve MySQL and backslash escape handling

This PR provides the ability to configure how jOOQ handles backslash escaping when dealing with MySQL databases. The PR provides three options:
* Assume that the database is not configured with NO_BACKSLASH_ESCAPES and always escape backslashes.
* Assume that the database is configured with NO_BACKSLASH_ESCAPES and don't escape backslashes (current behavior).
* Don't assume anything. Set NO_BACKSLASH_ESCAPES at the connection level. Don't escape backslashes.

More context: https://groups.google.com/d/msg/jooq-user/jCd7LjCs2vw/O8JiMFC24eIJ
Why not pass the context in here and then only call `.settings().getBackslashEscapeHandling()` in one spot?