[WIP] Made ico compatible with the latest version of populus and solidity

[voith]

What was wrong?

The ico repository was not compatible with the latest version of populus and solidity

How was it fixed?

• submitted fixes in py-solc repository: support solidity versions > v0.4.19 ethereum/py-solc#53, added flag evm-verison to solc_wrapper ethereum/py-solc#55.
• Have added some temporary fixes in populus to show what needs to be done to get the test suite green. I need to investigate a little about the best way to sub mit those fixes. Fixes in populus needed fixing the verify_contract_bytecode method and introducing evmVersion in populus
• updated solidity version in .travis.yml to 0.4.24.
• updated requirements.txt to pin the latest dependencies needed(There are some dependency issues with populus. However I fixed them by pinning them in requirements.txt)
• populus.json was ported to the new project.json
• evm_version was set homestead. Read https://medium.com/@chris_77367/explaining-unexpected-reverts-starting-with-solidity-0-4-22-3ada6e82308c for more details.
• Had to increase gas limit in tests TESTRPC_GAS_LIMIT = 6000000 as one test needs more gas. This seems wrong but I think this could be fixed. My suspect is populus which is not optimizing the bytecode as specified in populus.json. I verified this from the bytecode that was generated in .cache.

checklist before merging

• Make sure that populus.json has been properly translated to project.json.
• Ask @miohtama and @petri If this needs more manual testing before merging. TokenMarketNet might have dependent code based on this change. So I'd need some help with integration testing.
• submit fixes from my populus fork to the main repository and on merging the fixes make sure ico is pinned with a new release of populus.

[voith]

Marking this PR as WIP as some fixes from my populus fork need to be submitted upstream. All the tests are passing. I wanted to show case what changes are needed to get the test suite green!
cc @miohtama and @petri

[voith]

Update: I have added a new commit to this PR. For more context please see ethereum/populus#468. Earlier, I had fixed this in my fork. But since I found a workaround we don't really need to fix it!
New Checklist:

• I have opened a PR in populus to get past the issue populus raises BytecodeMismatch ethereum/populus#462 . Mark this done once the PR has been merged and a release has been created.
• Someone dropped python2.7 support in feature/465 drop support for python27 ethereum/populus#466. I will now review the PR. Once done I will ping @miohtama to merge both PR's.

[voith]

@miohtama Did you know about ethereum/populus#468. It seems like you added command_line_options feature in ethereum/populus#331.

[voith]

Update: It turns out that the setting optimer: true was not working. This was causing some tests to run out of gas. I have fixed this in a new commit: fb15afe

[voith]

closing in favour of #139