Include and use sqlite directly rather than the QtSql abstraction
Quassel needs to have sqlite support. Right now, we depend on Qt4 having sqlite support installed, which is not always the case. If Qt4 has been compiled without sqlite support, Quassel cannot be run.
We should therefore include the sqlite library within our sources and integrate it ourselves. This is encouraged by the sqlite people, and also made very easy because they provide a single *.c file containing all the code. We'd only need to compile this file together with the core to be able to use the lib.
Of course, SqliteStorage would have to be rewritten to not use Qt's SQL layer, but to use the lib directly.
Positive side effect: Make sqlite use utf8 instead of utf16. Since we mostly store strings, this should almost halve the size of the storage file.