Potentially explore having get_function be available as a decorator

`get_function` is repeated throughout every primitive. I purpose we explore the idea of making this available as a decorator instead which wraps the function needed to run in order to obtain the output. We could also add decorators for spark or dask specific functions as @rwedge mentioned.

ex:
```
class ExamplePrimitve
def get_function(self):
def example_function(x):
#some logic here
return something
return example_function
```

to

```
class ExamplePrimitve
@get_function
def example_function(x):
#some logic here
return something
```