Implement exclude_reblogs and include_rts

Adds a new exclude_reblogs parameter (default false) for our Mastodon API. I proposed this for Mastodon and it was just merged:

• https://github.com/tootsuite/mastodon/issues/9606
• https://github.com/tootsuite/mastodon/pull/9640

And the Twitter equivalent, include_rts, for the Twitter API (default true):

• https://developer.twitter.com/en/docs/tweets/timelines/api-reference/get-statuses-user_timeline

These filters will make it easier for frontends to show a user's original statuses, without including stuff they didn't write, in a similar spirit to exclude_replies.