flatten the structure by bringing services modules up and possibly merging some togther

[sbellem]

mainly for simplification purposes, such that instead of having something like:

class transactions.services.service.BitcoinService(testnet=False)

we can have something like:

class transactions.services.BitcoinService(testnet=False)

and perhaps, simplifying further:

class transactions.services.Bitcoin(testnet=False)

or alternatively:

class transactions.BitcoinService(testnet=False)