- Sets new target version to be 2.7.0.
- Updates dependencies to known-stable, forwards-compatible versions.
- Updates test matrix:
  - Test against v2 and v3 versions.
  - Run each against each supported PHP version.

This patch re-introduces the following classes from the
`Zend\Mvc\Service` namespace, along with related tests:

- `ConfigFactory`
- `ControllerLoaderFactory`
- `DiAbstractServiceFactoryFactory`
- `DiFactory`
- `DiServiceInitializerFactory`
- `DiStrictAbstractServiceFactory`
- `DiStrictAbstractServiceFactoryFactory`

It also re-instates the `ServiceManagerAware` and `ServiceLocatorAware`
initializers in the `ServiceManagerConfig` class (though they will now
emit deprecation notices), and ensures that class properly defines
services such that they'll be accessible identically between v2 and v3
of zend-servicemanager.

…eners

Not necessary with shipped, stable versions of zend-servicemanager.

- Re-introduced `createService()` method, proxying to `__invoke()`.
- Re-defined invokables as aliases + invokable factories.
- Re-enabled form abstract factory.

- Ensured each extend the appropriate v2 interface/class, and implement
  the required methods for both v2 and v3.
- Added `setInvokableClass()` implementation to `RoutePluginManager` to
  mimic work in `configure()` for v2.

Updated all factories to ensure they work with both v2 and v3 of
zend-servicemanager. Primarily, this consisted of re-adding the
`createService()` method as a proxy to `__invoke()`.

Updated all abstract factories to ensure they implement both the v2 and v3
methods.

Updated all plugin managers to ensure they implement both the v2 and v3
methods, define appropriate default services, and utilize the v2 properties for
"auto add invokables" and "share by default".

- Defer until after testing the instance, to allow injection in
  retrieved instances (vs lazy-instantiated ones).

Restores behavior to be backwards compatible; if the event manager,
request, and/or response are not passed to the constructor, they are
pulled from the service manager.

…ibility

Removed previous workflow from v2 with regards to:

- instantiation and initial configuration of the SM
- Retrieving the SM from the ServiceListener post-module loading (no
  longer necessary)

- Require zend-authentication 2.5.3 or up (first version to allow zend-stdlib
  3.0 support)

These changes provide basic v3 compability, allowing the tests to at least run
(though not pass). In particular:

- The `ConfigFactory` was only targeting v2 previously; it's now
  forwards-compatible with v3.
- The `RoutePluginManager` had two issues:
  - `configure()` had the wrong visibility.
  - `setInvokableClass()` is a method that changes signature between v2 and v3.
    Since the logic in the `RoutePluginManager` duplicates that in v3, it was
    removed.
- The EventManager factory, and any tests that were instantiating and injecting
  an EventManager with a shared event manager, received updates to allow varying
  instantiation based on version. v2 does not accept a shared manager to the
  constructor, and requires injection via `setSharedManager()`; v3 requires
  injection via the constructor, and removes the `setSharedManager()` method
  entirely.

- Updated `Forward` plugin to work with both v2 and v3 API of
  `SharedEventManagerInterface::getListeners()`.
- `ViewHelperManagerFactory` updates:
  - Fixed typo when registering Doctype helper factory.
  - All override factories now pull the parent service locator when under
    zend-servicemanager v2.
- Throw `InvalidServiceException`, not `InvalidServiceNameException`, from
  `DiStrictAbstractServiceFactory` (latter does not exist in v3)
- Test fixes:
  - `config`, not `Config`, service
  - `Request`, not `request`, service
  - do not grab return value of mutators on SM instances
  - use Prophecy to get SM/plugin manager instances (ensuring that constructor
    arguments can be ignored)