Added generic transform method

Instead of calling moving_average() when streaming data to NuPIC, we call
transform() method. We have also included an update() method, so transform has
two possible data transformations by now:
* moving_average: smooth data by moving_average_window before passing to NuPIC
* scale: scale data by scaling_factor before passing to NuPIC
Get display_names and use _transform()

We have a more general _transform() method call before sending data to NuPIC.

We also can get the name of some Librato sources now.
Using new _transform() method

Instead of calling _moving_window_average() we now call generic _transform()
method.

This allow us to do other kinds of transformations before sendind data to NuPIC.
Added new transform and scaling config

We also don't need moving_average_window to be passed, so it's optional now.

We accept a new configuration `transform`, which can be moving_average or scale.
Renamed average_value field to transformed

This reflects the latest changes on streams, allowing other transformations
besides moving_average.
Fix focus on ids with dots and rename average

Instead of Average, we now use Transformed in the legen.