Add support for SQLite databases

It would be nice if Joomla! would support the installation on SQLite databases.

This will make the SQLite driver selectable and contains some required modifications.

Note that the installation code has not been touched ('cause it changes oh so quickly :wink:), so you will get a somewhat rough "development experience" on installation:

* Choose `SQLite` in "Database Type"
* set a "Username" and "Password" even if those are not required..
* The "Database Name" must be the absolute path to you database file and has to be no longer than 64 chars....

This should be improved in future versions.
Some more information and thinking is in the [readme](readme-sqlite.md) file, some of them have already been implemented in the [sqlite branch](https://github.com/elkuku/joomla-cms/tree/sqlite).