Fixed bugs and layout adjustments

【Contents of the fix】
■Layout adjustment for tablet display
■【iPhone】Fixed a bug where the Hatena bookmark icon was not displayed on the share button in the fixed footer bar.
■Adjusted the layout of the staff list on the smartphone.

The following are the files that have been modified for this update.

【Modified file】
css/footer-bar.css
footer-bar.php
functions/update_notifier.php
languages/ja.mo
languages/ja.po
mobile/style-mobile.css
style-pc.css
style.css
widget/google_search.php

【Added files】
img/common/facebook.png
img/common/hatenabookmark-logomark.svg
img/common/line.png
img/common/twitter.png