Avoid using renderUI, as it is slow

[sckott]

I've recently cleared out some uses of renderUI #171

We still have ~ 15 instances of renderUI though on branch dev. Some of which are fine as they're doing something small, but for larger tasks we should avoid it's use.

I can't find a nice reference to this, but many SO posts and blog posts mention that renderUI is slow. It makes sense becuase it is used in the server side of Shiny, so you're rendering UI elements on the server, which is going to take more time than if you do it on the client.

In addition use of renderUI means that the UI element it creates is not there when the page first renders but at some later point, so it's a bad user experience - UNLESS the task is very quick then the lag shouldn't matter much.

Instead we should replace uses of renderUI with update* for whatever element type it is, e.g., updateTextInput