Added template model and foreign key.
tasks.render_template function.
SendEmailAsyncNow uses render_template, fix broken tests.
First working tasks.render_templates test.
Fixed accidental tasks commit.
Finished tests for render_templates.
Send text or html emails when appropriate. Plus tests.
Simplify tests for new template system.
New Template documentation.
EmailTemplates validation.
Updated readme for template rules.
Additional EmailTemplate validation rules.
`EmailTemplate.save` validation and test updates.
Merge pull request #3 from Wilduck/template-model

Template model