Feature request: support for selectors

[joeblubaugh]

I'd like to able to refine my :Kget by more than namespace when I have a long list of resources. Maybe one of these two approaches would work:

1. Another command similar to :Kns, :Ksel where you could add a list of selectors. :Ksel label1=value1 label2=value2. These selectors are applied to :Kget. I like this because it doesn't add more optional arguments to :Kget, but selectors don't really apply to other vimkubernetes commands like :Kapply.
2. Flags on :Kget, similar to the kubectl flags. Just let users write --selector label1=value1 --selector label2=value2 as part of their :Kget. This is less consistent with the rest of :Kget, which doesn't let you set flags like --namespace or --context.