Merge branch 'postgresql' into 'master'

Add postgresql support

Closes #3237

See merge request louiz/biboumi!18

Handle postgresql and sqlite3 libs properly

Do not fail to compile when one of them is missing but the other one is not.

Raise an error when trying to open a database with the missing library.

see #3237

Move biboumi.h.cmake inside the src/ directory

Refactoring louloulibs and cmake

Use OBJECT libraries
Remove the louloulibs directory
Write FOUND variables in the cache

Introduce an optional Database module

Uses litesql