Show filter when filtering

[friism]

Today I was looking at a user that had just pulled an image and then did this:

> docker images ls
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
>

Strictly speaking the output is correct because the user did not pull an image with the name ls which is what is filtered for. What the user meant to do was docker images or docker image ls.

To make this less confusing, I think we should display the filter when one is used. For example:

> docker images ls
FILTER: name=ls
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
>