simplify JdbcProfileProvider by removing "type JP" from base trait

[dholbrook]

Removing the type declaration from JdbcProfileProvider simplifies mixing in the JdbcProfileProvider trait. After the change ActiveSlickWithCodegen no longer has to override the type definition.

[djx314]

If remove the type JP, any way to access the slick extension when I need to use a specific driver ?
like https://github.com/tminglei/slick-pg
I need to use the type column[JsValue], so I can't use the common JdbcProfile.
See #26

[dholbrook]

This change caused existing code to break for me and at least one other person see #71

I found a workaround, by override the JP type, but it was non obvious why that was in there, and all the tests pass without it being there. I understand completely if this pr is rejected. It feels like there should be a cleaner solution, but I don't know what that would be.

[octonato]

Sorry that I couldn't react earlier. I had a busy day, too busy.

The JdbcProfileProvider was introduced exactly to make it possible to use alternative drivers, like slick-pg driver.

Therefore, we must maintain the type JP.

[octonato]

I'll add more documentation on that to avoid confusion.

[octonato]

Create an issue for it:
#73