Make critical sections of code that could introduce vulnerability be reviewed by at least 2 person with .github/CODEOWNERS

At least 2 person in case one of them is the author

i.e. modify the file https://github.com/AlphaWallet/alpha-wallet-android/blob/master/.github/CODEOWNERS

2 types of code should be covered:

* key management
* dapp browser, web3 provider injection and hook/callback handlers

Refactor, move a few files around if necessary?

iOS version https://github.com/AlphaWallet/alpha-wallet-ios/blob/master/.github/CODEOWNERS