Fix ORAI base denom and add images

[zhongfu]

Base denom should be 'uorai', not 'orai'; this denom is mentioned here too

[JeremyParish69]

Thank you for bringing this up. A few requests, please:
-also change "base": to "uorai"
-(Bonus) for the 6-exponent denom and the "display", make lowercase (the symbol being uppercase means that it will appear as uppercase throughout various UIs)
-(Bonus) upload the token logo images to the local repository under oraichain/images/orai.png + orai.svg

[zhongfu]

Done!

I've also taken the liberty to switch to the black logomark (i.e. logomark-light, png, svg), hope that's fine