Prefetch images and cache them

[LauraAubin]

I noticed that the first time an image is loaded it has a small delay. We could cache them the first time they are loaded so that this is not noticeable to the user.

Further more, we could implement prefetching for expected images. For example, we could prefetch the hover button once the quest is opened as it is very likely that the user will pause to read the quest, then interact with the buttons.

[LauraAubin]

Right now we are passing image urls to the image component to render the <img/> themselves. Instead, on mount we should create image objects for all urls so that they already exist and switching between them appears seamless.