Replace BCD API by TzKT API to fetch tokens

Context

Baking Bad recently announced their new API for tokens on TzKT, which should replace BetterCallDev's one in the end.

This MR implements the new API with the new tokens representation in the storage. The changes are straightforward following the new representation of tokens from TzKT and the new API changes. For the record the API is documented here.

This new API should be able to handle larger requests, but I've kept the numbers from BetterCallDev.

There's a Debug submodule in TokenAPI to test the two Tzkt's RPC and the decoding, that can be tested on the JS console:

readTokens(address)
readTokensNumber(address)

The MR will be in draft to avoid merging it with the debug commit.