transfer = ProposedTransaction(...) naming convention doesn't follow other libs

[alon-e]

both in iota.lib.js and iota.lib.java there are explicit transfer objects.
iota.lib.js
iota.lib.java

however, in iota.lib.py these objects are constructed with iota.ProposedTransaction(...), which is also used as an intermediary representation of transactions & bundles.
from examples:
https://github.com/iotaledger/iota.lib.py/blob/master/examples/send_transfer.py#L24

this is confusing for users moving from other library implementations. like myself. :)

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I propose a new class named Transfer, that inherits from ProposedTransaction and is functionally the same, but adheres to the naming conventions of the other libs. (without breaking code that already uses ProposedTransaction of course).

[todofixthis]

Hey Alon! Sounds reasonable to me. I'll add it to the 2.0.x branch.

[todofixthis]

Scheduled for release: 2.0.1