base: Further changes to base.html template blocks
templates: Adds base_single.html template which wraps the content in panel-success
allauth: Add email.html template for overriding
roots_tags: Add {% define %} template tag

Adds {% define %} template tag that is used for defining a template
variable with multiline content that is added to the template's context.

Within the template tag the content can also contain other template code,
including blocks which can be extended by the templates that are inheriting
from this template.
base: Add panel.html snippet for middle_panel
templates: Leverage panel.html with define blocks to avoid code duplication
base: Add content_wrapper block to the base.html template
templates: Add allauth's templates for overriding
allauth: Change templates to use base_single.html look
photologue: Add margin around photos in the gallery
competitions: Leverage crispy_forms in CompetitonRegistratonForm
base: Remove redundant template files from base directory