Select the domain (X-axis range) for charts before pulling data

Summary:
Depends on D20441. Ref T13279. Currently, we pull all the data, then decide what the X-axis should look like.

Since users will reasonably want to do stuff like "show me march-april 2018" in the future, we need to move toward flipping this around so that we can support cases where the domain is specified by the user.

For actual chart functions (like "constant(3)" or "cos(x)"), we must also know the domain before we pull data, since there are an infinite number of places where we can evaluate the function "constant(3)".

See note in T13279 about continunity.

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim

Maniphest Tasks: T13279

Differential Revision: https://secure.phabricator.com/D20442