Add events search bar in top nav

[alexwgraves]

Should use the same search logic as on the /events page. When a user enters a term and hits enter, it should take them to the /events page, where their results should be displayed (i.e. identical to if they had searched on the events page to begin with.

Style-wise, the search should be a search icon and should slide out when you click it (like on the DP homepage).