Implement configurable factory for creating MongoClient.

This allows for customization of the MongoClient creation.
Active play scala plugin, this got lost with commit a8ff9f46

Without the scala plugin the package does not contain any classes,
tests were not run as well (both due to the missing source settings).
Update test to target localhost, previously they failed.

Failure was this exception:

```
MongoTimeoutException: Timed out while waiting to connect after 9999 ms, took 10.648 sec
[error]     at com.mongodb.BaseCluster.getDescription(BaseCluster.java:114)
[error]     at com.mongodb.DBTCPConnector.getClusterDescription(DBTCPConnector.java:396)
[error]     at com.mongodb.DBTCPConnector.getServerAddressList(DBTCPConnector.java:355)
[error]     at com.mongodb.Mongo.getServerAddressList(Mongo.java:497)
[error]     at uk.co.panaxiom.playjongo.PlayJongoTest.assertMongoProperties(PlayJongoTest.java:46)
[error]     at uk.co.panaxiom.playjongo.PlayJongoTest.testMongoTestUriConfig(PlayJongoTest.java:33)
```
Merge branch 'master' of github.com:codemariner/play-jongo into codemariner-master
Merge branch 'codemariner-master'