vendor neutral implementation for pagination

[kivancsahici]

Hi Pavan,

First of all, many thanks for sharing your experience with the rest of the developer
community. Your spring-boot-datatable project was very valuable for me.

Under your blog post about this project, I saw many developers struggling to adopt
the code for DBs other than Oracle and MySQL. In this PR, I aim to

• remove any vendor specific code
• leverage JPA features for pagination in general
• make it easier for anyone who wants to run it locally. For that, I used an embedded DB.

Regards,
Kıvanç