Install Python packages in dependency order, not in parallel.

...and include a script to produce the proper ordering.

This was discovered while minimizing CircleCI steps to dianose a problem
with running the Launch Kit Backend in CircleCI.

These classes should be imported via the
zero_ex.contract_wrappers.exchange and
zero_ex.contract_wrappers.erc20_token modules, respectively.  We
permitted importing them from just zero_ex.contract_wrappers back when
they were the only wrappers we had, but now that we have so many
different contracts being wrapped, this is just another list to keep
manually updated (which, obviously is error prone, since it slipped
through the cracks already), so it's better to just not support this
type of import.

Without this, generated documentation was not including the class
members that represent the contract methods, rendering the usage
unclear.

...except for the dummy tokens.

Previously these teses were using 0xorg/launch-kit-ci, but that was a
one-off thing created just for CI, back before there was a regularly
maintained docker image of Launch Kit.

Changed to use 0xorg/launch-kit-backend since it's regularly
maintained/updated.

Because the -backend image is using a different Linux distribution
(Alpine), the commands used to wait for ganache startup also had to
change.

The tag used, 74bcc39, is provisional due to the pending Issue at
0xProject/0x-launch-kit-backend#73 .  When
that issue is resolved, the tag suffix on the imag name should be
removed.

Due to problem with launch-kit-backend, documented at
0xProject/0x-launch-kit-backend#73 ,
we need to checksum the makerAddress, in the order retrieved from the
relayer, before filling it, otherwise Web3.py gives this error:

InvalidAddress('Web3.py only accepts checksum addresses. The software
that gave you this non-checksum address should be considered unsafe,
please file it as a bug on their platform. Try using an ENS name
instead. Or, if you must accept lower safety, use
Web3.toChecksumAddress(lower_case_address).',
'0x5409ed021d9299bf6814279a6a1411a7e866a631')

Formerly CHANGELOG was in chronological order.  Now it's in reverse
chronological order.