Don't attempt to change "CachedUrls" table for units, that are not used in Mod-Rewrite URLs

1. add "adm:OnPopulateUrlUnitCacheScheduledTask" event, that would: - 0.5h

• • be a scheduled task, that runs once per hour
  • get values from "Prefixes" column of "CachedUrls" table of each database table record:
    • parse it's value (see "\kRewriteUrlProcessor::_setCachedUrl") to get unit config prefixes (ids doesn't matter)
    • collect list of unique unit config prefixes
  • store collected prefixes (even if it's an empty array) in "cached_urls_unit_prefixes" memcache key with 1 hour expiration

1. in the "\kCacheManager::incrementCacheSerial" method: - 0.5h

• • get value of "cached_urls_unit_prefixes" memcache key
  • if it's empty (either key is missing or an empty array is received), then consider it as array of commonly used unit config prefixes (e.g. "c", "lang", "theme", etc.)
  • if value of "$prefix" method parameter isn't within above retrieved/build array, then don't delete record from "CachedUrls" table

Quote: 1h*1.4 = 1.5h