Require pep8 now that we have a test dependency

* Since ccbdd82f3b420a535fb78f78a3695d584f784296, travis builds require
  pep8 to pass for the build to pass at all. This places the onus on the
  developer not to increase pep8 violations.
* Consequently, there is a practical dependency on having pep8 to do
  work on this codebase, even if there is no strict technical
  requirement for it.
* Install pep8 by default so developers can have more fun.
Create v3_dynamic certificate renderer.

Adds a new certificate renderer, v3_dynamic, which includes some of the improvements from previous Stanford renderers and is intentended to obsolete them:
- Rolling certificate date calculation, with pretty printing
- Dynamic text font selection for optimal aesthetics when different unicode sets are used
- Dynamic text sizing that tries to make names and course titles as large as possible
- Nice dynamic centering
- Also, introduces new semantics for 'interstitial texts' to allow them to be used not only to note distinction, but also the conditions for which a particular cert was granted
- Makes interstitial texts into a defaultdict which should make it safe to reference them everywhere without lots of annoying .get() failover
- Adding a test case in Travis for v3_dynamic certs with blank PDF template
Merge pull request #16 from caesar2164/giulio/new-soa-template

Add v3 dynamic cert template and logic
Merge pull request #27 from edx/jrbl/require_pep8

Require pep8 now that we have a test dependency
Refactor queue_xqueue
Add missing settings