Automatic custom skeleton dirs for crud, controller and form generators

Bug fix: no
Feature addition: yes
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: 
Todo: -
License of the code: MIT
Documentation PR: -

Important: This PR includes the merge of https://github.com/sensio/SensioGeneratorBundle/pull/166

Adds the possiblity to override skeleton templates for the next generators:

generate:controller

[entity's bundle]/Resources/SensioGeneratorBundle/skeleton/controller
app/Resources/SensioGeneratorBundle/skeleton/controller

generate:doctrine:crud

[entity's bundle]/Resources/SensioGeneratorBundle/skeleton/crud
app/Resources/SensioGeneratorBundle/skeleton/crud

[entity's bundle]/Resources/SensioGeneratorBundle/skeleton/form
app/Resources/SensioGeneratorBundle/skeleton/form

generate:doctrine:form

[entity's bundle]/Resources/SensioGeneratorBundle/skeleton/form
app/Resources/SensioGeneratorBundle/skeleton/form

If a template is not found it will use the default template in SensioGenerateBundle