[msg] filter msgs without attachments or bodies if ignoreBlankMessages is true

[sarahscott]

For https://artsyproduct.atlassian.net/browse/IN-56

Fixes #909

[mzikherman]

I'm not sure this is what we want, I think this logic needs to be implemented in Radiation, and the param passed through (from Metaphysics, to Impulse and then Radiation).

The reason is that the Relay pagination is going to get messed up otherwise- here the total count that we use in pagination (to determine hasNextPage, etc.) is coming from Radiation, and is counting even blank messages. That's why we should implement this upstream, that way the counts will be accurate.

[orta]

Deprecated by #918

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