template_pack in helper and removing cross references between template packs

* Allow to define a template_pack in a form_helper, which will override
`CRISPY_TEMPLATE_PACK`.

* All calls `render()` of a layout element should pass the template pack
* The `template` member of all layout elements should not point to a
hard-coded template pack. Even if a layout elements is only  relevant to
a single template pack, e.g. `MultiField` is only relevant to
`uni_form`. This will allow custom template packs to use these layout
elements.

* Remove cross references between template packs to make each template
pack independent from the others.

* Remove `MultiField` templates from `bootstrap` and `bootstrap3`
template packs (it's a `uni_form` template pack)

* Refactor some `uni_form` specific tests out of the general test cases.
Fixing 'Settings' object has no attribute 'CRISPY_TEMPLATE_PACK'
Fixed #245 -- The first ``AccordionGroup`` can now be set ``active=False``.

- If the user initializes the first ``AccordionGroup`` with the
  ``active=False`` kwarg, it will no longer be initially visible at
  page load.
- The original default behavior, which renders the first group when
  the ``active`` kwarg is not set at all, is still retained (and therefore,
  the change should be fully backwards compatible).
- Unit test written for new functionality.
- All previous unit tests pass.
Update crispy_forms_tags.py
Corrected text
Fixed bug #254 with respect to labels on form_show_labels.
Leave the default value to null to maintain compatibility #254
Remove debug #254
Handle None within layout as render nothing
Show label for checkboxes
Added rendering of wrapper class to inline radio select template.
Added myself to contributers.
switch away from deprecated setup_environ

- django.core.management.setup_environ has been removed in Django 1.6,
  django.conf.settings.configure is available since Django 1.4 and does
  the same
MultiField now obeys form_show_labels
Aligns buttons properly in bootstrap 3
Fix for button alignment for non-lg bootstrap classes
crispy_forms_tags.py: Fix typo

Signed-off-by: Sol Jerome <sol.jerome@gmail.com>
Merge branch 'bugfix/crispy_template_pack' of git://github.com/pkuhad/django-crispy-forms into dev
Merge branch 'master' of git://github.com/hekevintran/django-crispy-forms into dev
Merge branch 'dev' of git://github.com/tepez/django-crispy-forms into dev

Conflicts:
	crispy_forms/templatetags/crispy_forms_tags.py