Resources/Images are the icons used in Natron. They are not available on the binary distribution, it can only be changed at compile time. The icons are provided by Jean Christophe Levet. If you also want to propose some icons, you can make a pull request on the Natron github.
Regarding the layout of the interface, I'm afraid it's not going to happen, this is all coded in C++.
We already have plans and mockups for interface enhancements provided by Jean Christophe.
Note that you can however program your own panel with PySide in python though.