Django-crispy-forms

* Fix default value for `form_show_labels` in case FormHelper doesn't define it, see 199.
* Added a backported version of `override_settings` for testing django 1.3.7 and adding it to Travis-ci matrix.

Special thanks in this release to **Charlie Denton <a href="https://github.com/meshy">meshy</a>**, for his amazing support in PRs #189 and 190, long due.

* Deprecated `Tab` and `TabHolder` imports from `layout.py` module, they now live in `bootstrap.py` module.
* Removed Python 2.5 compatibility.
* Added `disable_csrf` helper attribute, see docs.
* Travis-ci support thanks to Charlie Denton, see 190.
* Python 3 compatibility thanks to Charlie Denton, see 189 and 190.
* Added a settings variable named `CRISPY_ALLOWED_TEMPLATE_PACKS` for adding easily support for new template packs, see 192.
* Added `{% crispy_addon %}` tag, see 195.
* Make `CRISPY_TEMPLATE_PACK` optional for tests
* Make tests run the same exactly way with `runtests.py` and `manage.py test`, see 183.
* Bug fix for `wrap_together` when using it with partial slices.
* Fixes for `KeepContext` context manager, see 180.
* Added `FormHelper.field_template` attribute, for easily override field template for a specific form/formset, see docs.
* Added a template for rendering formsets inline within tables named `bootstrap/table_inline_formset.html`, that can be easily used in conjunction with `FormHelper.template`.
* Added `FormHelper.template` attribute, that easily allows to override form/formset general structure template, see docs.
* Added `form_show_labels` helper attribute.
* Redoing filters to use `isinstance` instead of hacky internal name checking, this way subclasses of standard fields will work out of the box with crispy-forms, see 176.

* Bug fix for `KeepContext` context manager, when crispy-forms used with Jingo/Jinja2 templates, see 179.
* Some formset tests were breaking in some Django versions. Also added a `make test` for easily running project tests, see 178.

* Bug fix for model formsets and inline formsets, when being rendered with a `FormHelper` with a layout set, where some hidden formset management fields would be missing, breaking saving to database.
* Added `render_hidden_fields` attribute to `FormHelper`, see docs.
* Added `render_hidden_fields` attribute to `FormHelper`, see docs.

* Fixes to `Container` and `TabHolder`, affecting class variable helpers with layouts containing `TabHolder` or `AccordionGroup` objects, see 172.
* Bug fix for `KeepContext` context manager, see 172.

* Avoid raising Exceptions in `|as_crispy_field` filter when not in DEBUG mode.
* Popping `css_id` to avoid having a css-id attribute, see 167.
* Fixed a bug in dynamic layout API, when wrapping layout objects that had arguments passed after fields. Moving `LayoutSlice` to `layout_slice` module.
* Fixed test failing when tests runned from manage.py test.
* Fixed testing name conflict, see 130.