`Context` does too much

[cowlicks]

We'd like to have Context objects just be a way for engines to communicate with LocalArrays on the engines. Currently they also are for creating DistArrays, and cleaning managing managing data on the engines.

We should move array creation out of context, (see issue #35)

And let distarrays handle their own data. That is, make distarrays the proxy for handling data on the local arrays. Not Contexts.

[cowlicks]

I think we can close this once PR #252 goes in.

[kwmsmith]

Moving to the next milestone -- to fully refactor context will require more than a week's work.

[kwmsmith]

@cowlicks I'm in favor of closing this issue. We will be refactoring context down the road, and it's hard to say right now exactly what interface it will have. It will shrink, however.

I'd like it if we broke this issue into more specific issue or issues that are more clearly defined.

[cowlicks]

Sounds good