Add republican calendar support

[Mubelotix]

This is probably the first ever implementation of the republican calendar in Kotlin. It will be perfectly correct until gregorian year 2999, and provide estimates after that. I had to embed data for the start and duration of the years, as those can only be found from astronomical observations. It's less than 10kB. I chose to not take into account the time shift of around 15 minutes that occurred over the last 200 years due to errors in time measurement. (Yes, the time we currently use is off by 15 minutes.) I also couldn't take into account the timezone of the user as Birday only knows the date, not the precise time in the day

I had never used Kotlin before, so feel free to fix what's probably not very idiomatic. I have found the codebase to be very nice to dig into, even though I had trouble getting it to compile due to an outdated dependency that became unavailable over time. Thank you!

[Mubelotix]

Closes #314

[simonesestito]

I genuinely appreciate your work and dedication to this feature, but I have my strong doubts on how much this may be useful to an average user.

Moreover, I'm worried it may be confusing and hard to maintain with the future evolution of the project

But that's just my opinion

[m-i-n-a-r]

I appreciate your work and that's a really interesting concept,so first thing first, congratulations :)
Anyway, it's not clear to me how many users would use it. We have 2 possible approaches:

• wait to understand who would use this kind of calendar, and if more users are interested, I can merge the PR (despite the conflicts, it should be easy enough to resolve them)
• you can compile your version of "republican calendar Birday" (the license allows it if you quote the original author) and publish it wherever you want, if you prefer

I'm sorry to be so hesitant, but I want to make sure I only add things to the app that are used enough by users, avoiding making it too complicated

[Mubelotix]

It's a feature that indeed would only matter for french users. Most non-french people never heard about this calendar. I have found that french people were interested in knowing their birth date in this calendar when given the option, but never think about it by themselves. The good thing about this feature is that it will never require maintenance unless kotlin introduces breaking changes, and the code is pretty isolated from the rest of the app. The choice is yours, I will probably look into publishing it myself if you think that's best