Use sqlite helper plugin

All the sqlite database actions are rewritten to sqlite helper plugin.

The sqlite code of blogtng was almost similar to the sqlite helper plugin. All the differences are from improvements in the sqlite helper plugin.

I think there is no upgrade mechanism required. I reused almost all the sql database setup files. (only removed a bit that is default included in the sqlite helper plugin)

I have only tested this on an wiki that hasn't been a blog before. Also i have no experience with the blogtng. So i didn't test the syntax so far.

Please share the issues, then i can help fix them :)