Rendering in the Keybindings tab is extremely expensive

[ssorallen]

With a moderate amount of keybindings, filtering in the keybindings tab is pretty sluggish. Going from 1 character to 0 characters took 4s with the 'nuclide' package installed:

When filtering, each keybinding row is appended to a <table> that is already in the DOM. A small change of rendering the rows to a documetFragment and then cloning the complete fragment into the table would be minimal work and have a big impact on filtering cost.