Hidden tabbing

This is addressing issues mentioned in the comments of #638.

This branch adds a HiddenTabs component which is used on the manuscripts page – it differs from the existing Tabs component in that the tabs are not mounted and unmounted, but rather are hidden and shown. The effect of this is to cause fewer onBlur events to be fired in Wax editors; the context of the editor (undo stack, for example) is kept around.

The position of the tabs is static – so that you have to scroll up to see the tabs if you're in the middle of a tab. The tabs can be made sticky if a sticky prop is passed to HiddenTabsContainer in HiddenTabs.js. Not using the sticky implementation now because probably a better design should be applied to the page as a whole.

This is draft right now because I wonder if there are other tabs that this should replace.