Renaming /coherence/schemas.ex to /coherence/coherence.ex

[jung-hunsoo]

As many understood, the phoenix 1.3 has changed to reorganize the "model" things into contexts and its modules.

And the functions in /coherence/schemas.ex represent the "schemas.ex" as a context module, while it is called schemas.

This change won't improve its functionality but developers with coherence will have better readability for the codes.

[smpallen99]

I agree, I think context would be a more appropriate name.