Allow user API access in dev environments

This is achieved by allowing access if settings.DEBUG is True and
settings.EDX_API_KEY is not set or None (which is true for dev.py)
Allow user id filtering in user preference API
fixes back nav button
More xblock.save() calls to handle fields set during inits
E-mail notifications to users when course creator status changes.
Formatting updates.
Copy changes.
edx.org: adds in variables/mixins to support edx.org visual changes
edx.org: applies edx.org visual changes (with overrides/new mixins)
edx.org: handles letter-spacing on buttons
edx.org: revises iframe-based register/status buttons to match revised styles
edx.org: revising base link color variable to use darker value for accessibility
edx.org: abstracting new edx.org  button extends and colors with other themes in mind
edx.org: syncing up capitalization of register/login submit button copy
Merge pull request #486 from edx/talbs/mktg-vizsync

edx.org Login, Register, and iframe-based button visual sync
Merge pull request #501 from edx/gprice/user-api-tweaks

User API Tweaks
Ensure parent update of children decaches correctly
Merge pull request #505 from edx/dhm/xblock_save

More xblock.save() calls to handle fields set during inits
Studio course creator e-mails.
Merge pull request #488 from edx/christina/emails

Send e-mails when course creator status changes.