Upgrade solc to v0.4.17

[gnidan]

• Version bumps
• Warnings for internal Solidity code
• Update Truffle Boxes to remove warnings (this will have to go out after the full Truffle 4 release)

[gnidan]

Heads up about this, @DiscRiskandBisque @bmmpxf:

Solidity v0.4.17 adds keywords pure and view to replace constant, and now throws warnings if you don't explicitly indicate the visibility modifier for a function (external/internal/private/public)

The Truffle Boxes are all likely to cause two kinds of warnings with this solc version:

1. The compiler will warn to suggest view/pure in place of constant
2. The compiler will warn for visibility modifiers being missing.

Fixing the first issue will break compatibility, as older versions of Solidity don't know about pure and view. This will necessarily have to wait until the full Truffle 4 release.

The second issue can be addressed at any time, although I would say it is perhaps not likely a blocker for release.

[gnidan]

Closing because 0.4.18 is out. Moving to #628