Add SchemaBuilder

As promised, here is the **`SchemaBuilder`** to create/alter/drop table easily.

The code has all necessary Java doc and unit test coverage is 91% for classes and 96% for line coverage

I also added dependency to **`assertj`** with scope **`test`** so that assertions are more fluent than the classical **`assertTrue`**  and **`assertEquals`** 
Isn't it the other way around?