installation frontend javascript bugfix - win/xampp

Windows only issue:

The following issues appear when changing select-box for DB type in installation screen.

Solution: 

Using str_replace to replace **backslashes** to **forward-slashes** in case of SQLite. 
Windows PHP understands forward slashes correctly. 


The reason I submitted this is because of potential javascript error while installation to windows folder name starting with `x` :angry: letter (like in xampp). In essence - trying to set something like this:

```javascript
$('#config_db_name').val('C:\xampp\db\wolf.sq3')
```
the `\xam` part of the above string is treated as an escaped **octal code** in string and generates browser's **javascript syntax error**.

Converting path string to use forward slashes in PHP resolves this resulting in:

```javascript
$('#config_db_name').val('C:/xampp/db/wolf.sq3')
```

Additionaly, removed `#config_db_driver` **onchange** property which called non-existing fuction `db_driver_change` - this also generated **browser errors**.

Not essential but this may be very discouraging for people trying to install test SQLite Wolf in Windows ;)