Display current UV for Météo France results

[rthery]

Hello,

Météo France (and I guess probably other providers) just gives the maximum UV value during the day. I've added CommonConverter.getCurrentUV to get the UV at a given time, based on that value. Then I've used this helper method for Météo France results, but it can be used for other providers as well (as long as you know the time of the sunrise and sunset)

This is my first contribution to an Android app, so please don't hesitate to let me know if there are changes you'd like to see for it to be merged!

[papjul]

Very nice addition, especially in this season!

I didn't know about the formula, thank you.

[rthery]

Thanks!

For a bit of a context, it's just a very naive approach, based on the graph found on https://en.wikipedia.org/wiki/Ultraviolet_index
This won't take into consideration clouds for example, which can be a big contributor to the final UV index, but it should output the worst UV index with blue sky.
When I compared the computed value from the one from AccuWeather, it's either the same or just one index above. I think this is still better than nothing :) (my last sunburn would agree at least!)

[papjul]

Given the lack of reply from main developer, I decided to merge all currently pending pull requests in #440, so you can find your PR there, if you want to compile from source using the other enhancements/fixes