Fix performance regression causing unnecessary redraws

[fzaninotto]

Problem

Our context hooks (e.g. useListContext) always return new items, even though nothing has changed.

The problem is that they use lodash/merge, which is recursive. When merging complex objects, the result is almost always a new object.

Solution

Use lodash/extend instead.
Use lodash/defaults instead (because extend considers undefined values as an override, see https://stackoverflow.com/a/33247597/1333479)

Before

After

[djhi]

🔥