Investigate whether the memory usage of Dialog and FileDialog can be optimized

Investigate whether the memory usage of Dialog and FileDialog can be optimized. Currently it can use a fair bit even before it is visible, so if this could be reduced somehow then it would be good. Especially if elements can be cleaned up when it is hidden.

If nothing can be done, then documenting that they can use a fair bit and thus putting them into a Loader and reusing would be good.