[#3684] Polyfill support for version-dependent classes

- Per ideas from @ircmaxell, removed the conditional declaration of classes in
  favor of an autoloading solution. If using 5.3.3, composer will now load an
  alternate Zend\Stdlib\ArrayObject implementation.

  Both the project- and component-level composer.json files were modified so
  that the change will take place regardless of whether you install the full
  framework or just the component.

- Made changes to the php-code-sniffer configuration to ensure that the
  PHP-5.3.3-specific ArrayObject implementation is not checked, as it violates
  PSR-0 intentionally.

  - Realized that travis-build could be simplified, as .php_cs has the expected
    configuration for the full framework.
[#3684] Do polyfill for Session component as well

- SessionArrayStorage and Container were both doing version-specific conditional
  declarations; moved these into a compat layer as was done in Stdlib, and
  updated the composer.json for each of the component and framework.
- Currently, the SessionConfigTest suite is not running for me, but appears to
  be a random autoloading error from running in isolated processes; will see how
  the Travis-CI run looks.
[#3684] Simplified .php_cs fixers declaration

- A constant exists for what I wanted... Thanks, @Maks3w
[#3684] Fix indentation

- Fixes docblock indentation in compat file
Merge commit 'refs/pull/3689/head' of github.com:zendframework/zf2 into hotfix/3684
Merge pull request #3689 branch 'hotfix/3684'