Simplify Maniphest button filter toggle things

Summary:
Although these filters work pretty well, you still end up doing a double take
sometimes. Make the behavior simpler and more consistent by adding an "All"
button to "Open / Closed" so all three rows behave the same way (before, the top
row was toggleable but the other rows were select-only-one).

I played around with the styles a little bit too to try to make the selected
state more obvious.

sandra/anjali, let me know if this is good enough once it lands or if I should
go further in playing around with the styles and making it more clear.

Test Plan:
Filtered tasks with the various filter buttons, verified the task list
accurately represented the filters.

Reviewed By: tuomaspelkonen
Reviewers: tuomaspelkonen, jungejason, aran
CC: anjali, sandra, aran, epriestley, tuomaspelkonen
Differential Revision: 364