Allow a file to be fully loaded and displayed instead of clicking "Load more" multiple times

Currently, we load files by chunks of 500. This can be frustrating when dealing with very large files. An interesting solution could be to implement a "Load whole file" button. But, the code viewer is slow; it takes around 600ms to do the rendering of a 500 lines file in the DOM, 1.5 sec for 1500 lines. And we don't have any visual feedback that we are rendering.

We should either find a way to improve the rendering time so it's fast enough to not need a loader (could be the use of react-virtualized ?), or find a way to display a loader while the DOM is rendering.