Static top navbar instead of fixed

This change allows us to simplify the code in both
app.css and cleanup.php
Close #680 - Move Google Analytics to scripts.php
Update contributing guidelines
Update README
Updated polish translation
Remove WP Super Cache, add Soil to Recommended Plugins

Recommend only W3TC instead of both W3TC and Super Cache since it
could be confusing:

https://groups.google.com/forum/?fromgroups=#!topic/roots-theme/nOfLGhq90Ow
Merge pull request #681 from netboy/master

Update Polish translation
Use Bootstrap media object for listing comments

http://twitter.github.com/bootstrap/components.html#media

- Introduce lib/comments.php: contains Roots_Walker_Comment

- Update templates/comments.php to use the new walker, general
clean up
Merge pull request #683 from retlehs/bs_media_object_comments

Use Bootstrap media object for listing comments
Ref #652 - Add installation/config info to docs TOC
Remove disabled post nav links
Add section about grunt to README
Simplify alerts
Update editor-style.css

- Bring in latest Bootstrap changes

- Add instructions on how to update the file
Update danish lang files
Update CHANGELOG with changes since 6.3.0
Merge branch 'master' into grunt