Fix GTFS providers, rename/add GTFS cache fields

- Update GTFS provider to new ServiceProvider from 0.11
(comit c72772627ae30d6a45b856365d462c449cbcd447)
- Get modification time of the GTFS feed synchronously in
ServiceProviderGtfs::isTestResultUnchanged() (1 second timeout)
- Rename "feedLastModified" to "feedModifiedTime",
like done with ServiceProviderScript
- Add "feedUrl" to be able to check the modification time of the feed,
without having the provider data available, like done with
ServiceProviderScript ("scriptFileName")
- Fix old documentation for SerbviceProviderScript::runTests()