Better spongyCastle initialisation / decoupling

This is a follow-up for: https://github.com/walleth/kethereum/pull/21

There are now multiple of these blocks in kethereum:

    init {
        Security.insertProviderAt(org.spongycastle.jce.provider.BouncyCastleProvider(), 1)
    }

I would really like a cleaner way of initializing spongyCastle - and ideally a decoupling from sponygCastle from kethereum so it can also be used with bouncyCastle in a JVM context where the whole spongyCastle is not needed.

One Idea:

• create a kethereum-android module that has to be included when using kethereum in combination with Android
• inside this module there is a content-provider that initializes spongyCastle

@mirceanis what do you think?

[ligi]

Was recently talking to @cketti recently and I think he is correct that the best way is not to use the providers at all but the lower bouncycastle API - so we do not need the split spongy/bouncy at all. This way we also can avoid the multiple insertProvider calls. Perhaps when doing so we can also hide bouncycastle behind some crypto-interface so we can replace it with a pure Kotlin implementation at a later point.

[mirceanis]

The ContentProvider sounds like a good idea to try. Firebase does the init that way and I remember they had a few problems in the beginning. A successful completion of this would have to account for that and avoid it.

A link to start one off: https://firebase.googleblog.com/2016/12/how-does-firebase-initialize-on-android.html