Feature/session expiration

Use new SessionInactivityExpiration RequestContext subclass for SDK calls made in sectioning (by swapping out parent class for subclass in utils).  Add config setting to expire sessions after certain amount of inactivity to production settings file.
I tried adding the version to the end of the line, but pip failed to install the sdk dependency.  I wonder if there is some peculiarity with how dependencies are defined in a requirements file vs. in the setup.py?  Either way, it only worked when I took off the version ending.