fix(style): tos/pn layout overlap
Merge pull request #1827 from mozilla/issue-1748

fix(style): tos/pn layout overlap
fix(avatars): load profile image on settings and sign in pages if available

Fixes #1727.
fix(avatars): ensure the default image background is covered by the profile image
refactor(avatars): remove Session cache and load avatar from server
refactor(Session): use User and Account models in lieu of Session

This refactor changes a number of things:
- introduces User and Account models
- imports old Session based sessions into User
- handles direct link to settings page from RPs for a specified account (fixes #1686)
- redirects unverified accounts that visit /settings (fixes #1716)
- introduces a way to pass ephemeral data between views
- removes unused avatar-change-via-URL resources/tests (fixes #1544, fixes #1618)
refactor(account): User always returns an account; no more null
refactor(views): use private var notation and othe clean-up
tests(settings): more functional tests coverage of settings page

Adds tests for issue #1716 and #1686.
refactor(account): update fx-desktop broker to work with user and account models