Google Sitemap support

The commits, which code must be used as base for plan implementation (of course move code from Custom module to Core):

• rEBN16353, rEBN16370, rEBN16606 - adds Google Sitemap functionality
• rCCD15674, rPLS18795 - show specified categories only in debug mode

Plan

1. apply modification to kThemesHelper class, that was made in INP-1229 task that used SimpleXML instead regex to parse template meta info in "kThemesHelper::parseTemplateMetaInfo" (don't add "section"), but don't add "section_aware/section_agnostic" to allowed parameters
2. add the "in_sitemap" to allowed parameters
3. normalize value in "in_sitemap" setting using following logic:
   • no value (can use "empty" function to detect it) - return boolean true
   • value is any of "yes", "true" (as string), "1" - return boolean true
   • value is any of "no", "false" (as string), "0" - return boolean false
   • anything else - throw an exception
4. add the "IncludeInSitemap" column to "Categories" table:
   • usual DB type for checkboxes
   • defaults to 1
   • and "c" and "st" units
   • show on category add/edit template (see rEBN16370)
5. in the "CategoriesEventHandler::_prepareAutoPage" method based on $template_info['in_sitemap'] value (only if such key present) set the "IncludeInSitemap" field of created category to 1 or 0
6. add following system setting to "Configuration > Website > Output" section's "General" sub-section after "CategoryPermissionRebuildMode":
   • setting name: SitemapInvisibleCategoriesCatalogVisibility
   • title: Sections hidden from Sitemap
   • displayed as: radio buttons
   • options:
     • 1 - "Always Shown in Catalog" (default value)
     • 2 - "Shown in Catalog Only in Debug Mode"
7. hide categories with "IncludeInSitemap=0" based on "SitemapInvisibleCategoriesCatalogVisibility" setting (compared to code from rCCD15674 we'll be looking at "IncludeInSitemap" column instead of adding "ShowInDebugModeOnly" column):
   • in Admin Console category grids (regardless of Special)
   • in category dropdown (e.g. parent category selection during category editing OR internal page selection during link adding via CKEditor)