Multiple database engines

[bruntib]

In #359 the --database flag has been eliminated from under CodeCompass_webserver. This connection string is unique for different projects, so this connection string is stored in the workspace directory for every project. This indicates that different projects could connect to different database engines (currently PostgreSQL and SQLite are supported). However, the .sql files are generated only for one engine at the same time. We could leave this limitation by generating .sql files for both database engine format.

I think this should be a low level priority, best effort ticket. The subtasks are:

• [ ] Generating .sql files both for PostgreSQL and SQLite.
• [ ] Eliminating -DDATABASE flag from CMake build system.
• [ ] Check if the .sql files are really necessary. ODB is able to create tables from C++ code as well. The only reason why we use .sql files is that we want to separate the process of adding indexes to the database after parsing. We should check if it is possible from C++ code.

[whisperity]

Right now in #385 it seems that having multiple libraries linked against the binary brings forth some magic issues...