Fix remaining bugs for python 2.7

appveyor.yml

beem/amount.py

beem/blockchainobject.py

beem/comment.py

beem/price.py

beem/transactionbuilder.py

beem/vote.py

beem/wallet.py

beem/witness.py

beembase/objects.py

beembase/operations.py

beembase/signedtransactions.py

beemgraphenebase/account.py

beemgraphenebase/base58.py

beemgraphenebase/bip38.py

beemgraphenebase/dictionary.py

beemgraphenebase/ecdsasig.py

beemgraphenebase/objects.py

beemgraphenebase/signedtransactions.py

beemgraphenebase/transactions.py