Issue #1888424 by katbailey, steveoliver, twistor, beejeebus, effulgentsia: Change notice: Make Drupal's URL generation logic available to HttpKernel, and minimize code repetition/divergence.

Issue #1976180 by katbailey: Fixed url_alter_test() module uses an event subscriber instead of a path processor.

Issue #1862024 by katbailey: Remove all references to hook_url_inbound_alter() as it is no longer invoked.

Issue #1269742 by katbailey, beejeebus, pwolanin, g.oechsler, ksenzee: Make path lookup code into an pluggable class.

Issue #1608842 by chx, alexpott, sun, effulgentsia, beejeebus, tim.plunkett et al: Replace list of bootstrap modules, enabled modules, enabled themes, and default theme with config.

- Patch #1183208 by effulgentsia, Niklas Fiekas, katbailey, no_commit_credit, catch: remove variable_get()('clean_url()') and switch to index.php/path pattern for dirty URL support.