All Symfony requirements set to 2.6

* Avoiding some security issues
Added final to all static-access classes
Issue #371

* Added enabled parameters in some extensions
Merge pull request #379 from elcodi/hotfix/final-classes

Added final to all static-access classes
Merge pull request #381 from elcodi/hotfix/added-enabled-parameters-extensions

Issue #371
Merge pull request #376 from elcodi/feature/symfony-2-6-requirements

All Symfony requirements set to 2.6
State Transitional Machine for Elcodi.

This is an implementation of a State Transitional Machine and the intergration
with given Elcodi implementation.
Merge pull request #375 from elcodi/feature/state-transition-machine

Feature/state transition machine
Fixed state transition machine composers
Merge pull request #385 from elcodi/hotfix/state-machine-composer-definitions

Fixed state transition machine composers
fix travis environment for tests
Merge pull request #387 from xphere-forks/fix/migrate-symfony-2.6

Fix travis environment for tests
undress AbstractExtension
extract `getConfigTreeBuilder`
better test fail messages on exception
avoid errors when $application is not defined