No isFork optimization

[zardoy]

repositores field in GitHub GraphQL Api supports isFork arg, by using which we can significantly reduce calls to this API (thus fetch all repos faster), however the forks filter button is too flexible. In other words user always can toggle forks visibility and the cost of fetching only forked repos and then full repos refetch it too high.

Maybe I should have retained Open Forked Repository... command. Which would've worked much faster but in the cost of less flexibility. Also this button looks kinda stupid, but I like this fast filter.