Add rake test and rake store:flush

Adds rake test as well as

### rake progressrus:store:flush[scope]

This rake task is currently only working in 


### dependencies

Currently, this rake task is dependent on an `environment` task and assumes the store is set up ahead of time.  Gives the ability to do

``` 
rake progressrus:store:flush[maintenance]
```
In order to `flush` all `maintenance` scoped redis keys.

```
rake progressrus:store:flush[1,maintenance]
```
to flush a multi-part key.


Also adds a railetie to expose the rake task to rails projects