Support for dynamically included templates

[eliasdorneles]

Hello!

Thanks for writing and sharing this library, it's pretty handy! 👍 🌮

I've bumped into an issue when using a dynamic include like {% include variable_pointing_to_a_template_path %} -- which is supported by Django, but fails with TemplateDoesNotExist when you run get_node_instances(...) on a template that contains that (see example project attached).

I believe it would be a better behavior to skip loading the template in these cases (when it's a dynamic variable instead of a hardcoded path).

This is the Traceback:

>>> from django.template.loader import get_template
>>> from django.template.base import VariableNode
>>> from template_analyzer.djangoanalyzer import get_node_instances
>>> tmpl = get_template('index.html')
>>> get_node_instances(tmpl, VariableNode)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/elias/.virtualenvs/web/local/lib/python2.7/site-packages/template_analyzer/djangoanalyzer.py", line 243, in get_node_instances
    return _scan_nodes(nodelist, context, instances)
  File "/home/elias/.virtualenvs/web/local/lib/python2.7/site-packages/template_analyzer/djangoanalyzer.py", line 158, in _scan_nodes
    results += _extend_nodelist(node, context, instance_types)
  File "/home/elias/.virtualenvs/web/local/lib/python2.7/site-packages/template_analyzer/djangoanalyzer.py", line 114, in _extend_nodelist
    results += _scan_nodes(block.nodelist, context, instance_types, block, ignore_blocks=all_block_names)
  File "/home/elias/.virtualenvs/web/local/lib/python2.7/site-packages/template_analyzer/djangoanalyzer.py", line 182, in _scan_nodes
    results += _scan_nodes(subnodelist, context, instance_types, current_block)
  File "/home/elias/.virtualenvs/web/local/lib/python2.7/site-packages/template_analyzer/djangoanalyzer.py", line 147, in _scan_nodes
    template = get_template(node.template.var)
  File "/home/elias/.virtualenvs/web/local/lib/python2.7/site-packages/django/template/loader.py", line 25, in get_template
    raise TemplateDoesNotExist(template_name, chain=chain)
TemplateDoesNotExist: template_point

Here is the content of the main templates showing the issue (attached a full project reproducing it):

$ cat myapp/templates/index.html 
{% extends "base.html" %}
{% block body %}
<h1>block index</h1>
{% with template_point="t1.html" %}
{% include template_point %}
{% endwith %}
{% endblock %}

$ cat myapp/templates/other.html 
{% extends "base.html" %}
{% block body %}
<h1>block other</h1>
{% with template_point="t2.html" %}
{% include template_point %}
{% endwith %}
{% endblock %}

testingproj.zip