Replace Proxool by HikariCP

[chrjohn]

Proxool is not maintained anymore.

Replacing it with HikariCP should be relatively easy.

Also see #607 #613 #373

[the-thing]

You can assign to me.

[chrjohn]

Great, thanks Marcin. 👍
Edit: it shouldn't matter but in the long term (maybe even for 3.0.0) I'd like to move the JdbcStore stuff and its dependencies to a separate module in another repo.