Add utils and tests for domain exceptions to blocking
Ignore and inject cookies for domain exceptions
First pass at panel UI for domain exceptions

Implementation:
* domain exceptions show up as usergreen on the page that they're exempted for
* clicking on "undo" button on the exempted page deletes the domain exception
(in addition to resetting the tracker state globally)

otherwise shows up as usual on non-exempted pages.
Start making domainException popup UI
Merge branch 'master' into feature/issue-165
Merge branch 'feature/issue-165' of github.com:EFForg/privacybadgerfirefox into feature/issue-165
refactoring to make domain exception popup work
Merge branch 'master' into feature/issue-165
remove "allow on this page" from domain whitelist popup. fix tab reloading.
Merge branch 'master' into feature/issue-165
style tweaks and refactoring as per comments from @jsha on pull request #256
remove unused css file
more fixes as per @jsha's suggestions in #256
more changes as per comments from @jsha
Merge pull request #256 from EFForg/feature/issue-165

Feature/issue 165