Advances #165.

Make save_button template customizable with parameters.

See merge request AlekSIS/AlekSIS!133

Add fields to CONSTANCE_ADDITIONAL_FIELDS

See merge request AlekSIS/AlekSIS!132

Add fields for:
	- Integers
	- Passwords

Add block for hiding page title tag

See merge request AlekSIS/AlekSIS!131

Drop opinionated settings for PWA

Closes #140

See merge request AlekSIS/AlekSIS!130

Let model extensions define new fields

See merge request AlekSIS/AlekSIS!129

* Base URLs are set to / in PWA's default settings anyway
  * With https://github.com/silviolleite/django-pwa/pull/32 merged, the defaults will
    work under all circumstances without changing settings
* l10n/i18n assumptions should not be made. PWA will see another MR to enabled
  it to use the language settings used in Django

Closes #140.

ExtensibleModel is now an abstract base model.

Advances #141.

Add weekday field for constance

See merge request AlekSIS/AlekSIS!128

Bug fix for merge_app_settings

See merge request AlekSIS/AlekSIS!127

Update contribution guidelines

See merge request AlekSIS/AlekSIS!126

Without this bug fix the function doesn't import the settings module but the apps module.

Also, restructure a bit on the go.

Move path_and_rename to core_helpers.py and delete old helper.py

See merge request AlekSIS/AlekSIS!125

Load calendar labels from calendarweek library

See merge request AlekSIS/AlekSIS!122

# Conflicts:
#   pyproject.toml

Resolve "Background Tasks / Task Broker"

Closes #154

See merge request AlekSIS/AlekSIS!123