www: Add vote status query param onto get vetted

[lukebp]

When the proposals view initially loads it fetches a page of vetted proposals from politeiawww. The problem is that we list the proposals in the GUI by vote status, so despite the "pre-voting" tab showing that there are 12 pre-voting proposals, its possible that none of these proposals were in the original page of vetted proposals that were fetched from politeiawww. This means that navigating to the "pre-voting" tab would reveal a list of 0 proposals and would just show the "Load More" button. This is not ideal.

Adding an optional votestatus query param onto GET /proposals/vetted would allow the GUI to fetch a page of proposals of a certain vote status, ensuring that each tab of the proposals view is able to be populated correctly on initial load.

[victorgcramos]

As we discussed on Slack, I'll be working on this issue from now.

[lukebp]

#795 makes this no longer needed.