load from 3dstreet json only works once per session

[kfarr]

To reproduce:

• load app, open modal, click Upload 3DStreet JSON File, upload a file and see the scene load successfully
• open modal again, choose a different 3dstreet json file, note that no scene is loaded

workaround:

• reload the entire app to load the scene from 3dstreet json

instead: it should load as expected

[vincentfretin]

There is also something wrong with this button, you really need to click on the text, not the background.

[vincentfretin]

For the clickable area, I fixed it in #856