Stellar: expand client calls

We need more functionality from the stellar client:

[x] Ability to get information of your account (transactions, address, public key, etc.)
[ ] Allow creating a new account on stellar and activating it (is dependent on https://github.com/threefoldfoundation/tft/issues/240)
[x] Selling / Buying TFT with XLM
[x] Sending tokens to another address
[x] Add examples in V

threefoldtech / web3gw