[cms] Add line item payout summary commands

[alexlyp]

This command allows administrators to query the cms database for
all paid out line items within a given period of time. This will be
used to create public summaries of expenditures by domain for any
given month.

[lukebp]

Code LGTM. My only comment is that you're killing me with the 80 column limit. We treat it as a hard limit in the politeia repo. You really need to add a visual cue to your editor to mark column 80 so that I don't have to keep leaving the same comment.

[alexlyp]

OK looked for any possible 80 char over limit. Understood. While I do have a 80 char limit marker set up, I didn't realize that it was such a hard rule. Will be more aware moving forward.

[lukebp]

Much appreciated!