Adding a date range opacity prop for light mode

[crussell122]

Per #85, added an optional rangeOpacity prop to allow for different opacity levels for light mode.

p.s. This is my first time ever contributing to an open source project so feedback is welcomed!

[RichardLindhout]

@crussell122 Hey thanks for your commit! I was busy lately so haven't seen in yet. I would rather follow specifications of Material Design on this or do other opacities for light/dark mode. Is it ugly in your app?

We need to check with the color library if the color is dark and use other colors I think

[iM-GeeKy]

Let's close this. The user that opened this was helping out on my side project and this is no longer relevant. We should just follow Material guidelines as you've mentioned.