Problem: inconsistent logic regarding experimental gravity module in genesis import/export

[yihuang]

Found by @JayT106

When not passing --unsafe-experimental flag, the current behavior is like this:

• init genesis, the genesis file does include gravity section
• export, the output genesis file doesn't include the gravity section
• validate-genesis, will fail if it doesn't include the gravity section

The root cause is the global app.ModuleBasics always includes the gravity module disregarding the experimental flag.

Change the validate-genesis and export command to have correct module list according to experimental flag.