More initialism corrections (golint)

More initialism corrections (golint)

Thanks to @bep's new, brilliant helpers.Deprecated() function,
the following functions or variables are transitioned to their
new names, preserving backward compatibility for v0.14
and warning the user of upcoming obsolescence in v0.15:

 * .Url → .URL (for node, menu and paginator)
 * .Site.BaseUrl → .Site.BaseURL
 * .Site.Indexes → .Site.Taxonomies
 * .Site.Recent → .Site.Pages
 * getJson → getJSON
 * getCsv → getCSV
 * safeHtml → safeHTML
 * safeCss → safeCSS
 * safeUrl → safeURL

Also fix related initialisms in strings and comments.

Continued effort in fixing #959.