_s: Simplify entry meta output

- Fix entry-footer inconsistency between content-*.php files
- Move in a function <code>_s_entry_meta()</code> to avoid duplication

---

At the moment there is an inconsistency between content.php and
content-single.php regarding the .entry-footer output.

In my opinion content.php output is would be better to use because it's
easier to translate and allow more customisation.

Finally by moving it into <code>inc/template-tags.php</code> we are
getting rid of some duplicated code.
Removed vendor prefixes, except where it fixes a specific bug or quirk
Adds in missing class

Brings in class that was missing from updated Sass but in style.css.
Props @corvannoorloos
Put vendor specific property first
Update _mixins-master.scss
Merge pull request #568 from fsylum/master

Reordering vendor-prefixes property in the mixin: props @fsylum
Puts width in right place

Props @corvannoorloos
indentation using tabs instead of mixed tabs/spaces

see https://github.com/Automattic/_s/pull/565
Update input field border color

now matches style.css
Merge pull request #570 from corvannoorloos/patch-1

Indentation using tabs instead of mixed tabs/spaces- props @corvannoorloos
Merge pull request #571 from corvannoorloos/patch-2

Update input field border color props @corvannoorloos
Prepare Underscores for Coding Standards. See https://github.com/Automattic/_s/issues/553.
Update archive.php

Revising the "primary" element to use a "div" vs. "section" to bring it into sync with index.php and single.php
Prepare Underscores for Coding Standards. See https://github.com/Automattic/_s/issues/553. [skip ci]
Merge pull request #581 from philiparthurmoore/master

Introduce Coding Standards Checks into Underscores
Kick off Travis CI Build Monitoring for _s

See https://github.com/Automattic/_s/issues/553.
Changes description of mixin - props @r007

Relates to #582
Rewording "plugin" to "theme"
Merge pull request #586 from yoarts/patch-1

Change plugin references to theme references in Travis CI config file.
Add fixes for faulty Sass @import paths and negative values.