Proper handling of fixed-point types

[clangenb]

Currently we have defined our fixed point types like:

BalanceType: i128

but what is returned from the chain is:

BalanceTypeChain: {
     bits: i128
}

We need to somehow align this properly such that:

• To the outside; the developer does not see a difference, whether he is using encointer-js or polkadot-js/api directly.

Which basically means that we need to change the encointer-js code to BalanceTypeChain as arguments and return values of its function.

We need to update the code at several places to fix that.