Add script that more efficiently imports large files.

I was running into resource issues trying to import a sql dump ~500M(output below). In order to get around this I changed the import script to use a `ReadableStream` instead of `fs.readFileSync`. Because this makes reporting progress a little more difficult, I put it in a separate file to keep that available.

Thanks!

```
[etherpad@etherpad bin]$ node importSqlFile.js output.sql
[2013-05-14 21:58:47.904] [INFO] console - 0.319
initializing db
[2013-05-14 21:58:47.912] [INFO] console - 0.327
done
[2013-05-14 21:58:47.912] [INFO] console - 0.327
open output file...
FATAL ERROR: CALL_AND_RETRY_0 Allocation failed - process out of memory
```