Openwisp-controller

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- [controller] Added ``NETJSONCONFIG_REGISTRATION_SELF_CREATION``
- [models] Handled accidental duplication of files across templates
- [controller] Update hardware device info during registration
(if the device already exists, the registration will update its info)
- [admin] Moved ``hardware_id`` field in device list admin
- [bugfix] Fixed broken preview when using ``hardware_id`` context var
- [models] Flagged ``hardware_id`` as not unique (it's ``unique_together`` with ``organization``)
- [admin] Hidden device configuration context field into advanced options
- [models] Removed LEDE from the OpenWRT backend label
- [docker] Added ``REDIS_URL`` to docker-compose.yml and settings.py (for dev and test env)

--------------------------

- [models] Improved consistent key generation, now a consisten key is generated
also when creating devices from the admin interface (or via model API),
before it was only done during registration
- [admin] Fixed unsaved changes JS bug that was triggered in certain cases
- [deps] Switched back to jsonfield

--------------------------

- [deps] Upgraded to django 3, upgraded dependencies
- [deps] Dropped support for python 2
- [x509] Fixed serial number max length (imported from django-x509)
- [admin] Fixed bug that caused organization field to be missing
when importing a CA or certificate

--------------------------

- [feature] Added connection module (possibility to SSH into devices)
- [feature] Added default operator group
- [feature] Added management IP feature
- [change] Changed configuration status: ``running`` has been renamed to ``applied``
- [admin] Added ``NETJSONCONFIG_MANAGEMENT_IP_DEVICE_LIST`` setting
- [admin] Added ``NETJSONCONFIG_BACKEND_DEVICE_LIST`` setting
- [x509] Fixed common_name redundancy
- [admin] Hidden "Download Configuration" button when no config is available
- [controller] Register view now updates device details
- [deps] Added support for Django 2.1 and Django 2.2
- [models] Added support for hardware ID / serial number
- [device] Add context field to device
- [bugfix] Show error when the preview is experiencing issues
- [ux] Group device change form in tabs
- [ux] Show loading indicator while loading preview
- [vpn] Add controller views (download & checksum) for VPN config
- [vpn] Fixed DH params in preview 107
- [change] Moved urls to admin namespace
- [feature] Implement copy/clone templates
- [feature] Added API to get context of device
- [bugfix] Ensure atomicity of transactions with database during auto-registration

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- [requirements] Updated requirements and added support for django 2.0

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- [pki] Reimplemented serial numbers as UUID integers
- [pki] Added switcher that facilitates importing certificates
- [pki] [admin] Removed ``serial_number`` from certificate list