Allow Objects as Values For Select Component

[rtablada]

This implements both #30 and #31.

For implementation this uses a yielded child component which also gives an upgrade path for users of embers-select (a mostly deprecated community component).

There is a breaking change since this changes the order of arguments sent to onChange (#30) and sends the full object value of the selection option rather than the string attr value.

[rtablada]

Merging this would close #43

[hergaiety]

Took a glance at the code and it's looking really really good. Would recommend going in and cleaning up the indentation as in github it looks like things are at different indentation levels. Could be an IDE difference.

That along with some documentation upgrades, and I'll clone things down locally just to double check stuff, but this looks great and should be mergable soon I imagine.

EDIT: By the way, CI will likely fail due to #42 but that won't block us from merging this PR, we'll just make note of what Ember versions are supported and address that issue separately.

[hergaiety]

I love seeing this logic extracted to its own sub component, well done!

[rtablada]

Updated whitespace in the effected files to match the standard Ember editorconfig (2 spaces). The test file had some existing mixed tabs and spaces.

Will look at docs in the morning!