Update Crayon Syntax Highlighter to 2.6.1
Revert "Install Lazy Load 0.5"

This reverts commit 121463b2f0c210e92678c047a273d0c446c6cfa7.

Because Lazy Load breaks the rendering around future images.
Revert "Install Head Cleaner 1.4.2.11 plugin"

This reverts commit c652114131e2a292f1abe43393aed93a77ce8a56.

Because Head Cleaner doesn't support Jetpack Carousel.
Revert "Ignore Head Cleaner cache dir"

This reverts commit 84b7794d52ed4eec9189608cb9156762434e459e.

Because Head Cleaner was uninstalled.
Expand line-height of hn

All default line-height is 24px but they are too narrow for Japanese.
New values, 1.6X is narrower than 1.6X as the content's line-height,
because the title doesn't has many lines.
Delete text-align: justify when the window width is <510px

Because text-align: justify is hard to read at small window.
Move $table_prefix to wp-db-config.php

Because $table_prefix is different between development site and production site.