When setting the start and count values for the `RebuildStaticCacheTask` the limits are ignored because the $urls variable is never reused after it is defined.
This also changes getObjectsToExport() to getExportUrls() to allow extensions to provide plain text url's for Director::test().
Pushes the controller to dev/staticexporter as some framework install doesn't include default class routing.
The error-XXX.html pages generated in assets folder use the dynamic URL
so they can't be used on the frontend. Provide a copy of these in cache
folder during the publisher processing task.
