"Modernize" the MOI wrapper

[odow]

This package needs to be updated to MOI v0.7. In addition, there are a lot of things that should be fixed to keep up with other changes in MOI:

• A large amount of the tests are excluded because the MOI wrapper doesn't support names: https://github.com/JuliaOpt/Cbc.jl/blob/master/test/MOIWrapper.jl
• There are lots of type-stability issues, e.g. https://github.com/JuliaOpt/Cbc.jl/blob/414499ee73b7679f4aff6b420a91ad270be8d87a/src/MOIWrapper.jl#L369-L372 which will return nothing instead of throwing an error.
• The wrapper should be updated to reflect the latest style guide

[mlubin]

The title is out of date given #91, but the points are still relevant.

[odow]

Closed by #108.