[NodeBundle] Added 3 new helper methods

[tentwofour]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Fixed tickets

Added 3 new helper methods to NodeMenu:

• getSiblings($node)
• getNextSibling($node)
• getPreviousSibling($node)

Useful for things like linear-style nav (in my case, Next Project/Previous Project), while retaining progressive enhancement.

Some simple template logic, once nodemenu is defined:

{% set currentNode = nodemenu.getCurrent() %}
{% set nextSibling = nodemenu.getNextSibling(currentNode.node, false) %}
{% set prevSibling = nodemenu.getPreviousSibling(currentNode.node, false) %}
                    {% if prevSibling %}
                        <a data-pager="prev"
                           href="{{ path('_slug', {'url': prevSibling.nodeTranslation.url }) }}">
                            ({{ prevSibling.nodeTranslation.title }})
                        </a>
                    {% endif %}

                    {% if nextSibling %}
                        <a data-pager="next"
                           href="{{ path('_slug', {'url': nextSibling.nodeTranslation.url }) }}">
                            ({{ nextSibling.nodeTranslation.title }})
                        </a>
                    {% endif %}