Devflow 1.2.0 Minor Release

Devflow 1.2.0 minor release includes some bug fixes along with removing the `App` directory and replacing it with a core submodule. Themes is a new featured added to this version as well. You can install themes via composer and then enable a theme in the backend. To test out the new theme functionality, install the Vapor theme.

• Removed unused imports in db helper
• Core is now a composer component/submodule
• Fixed issue with loading all the .mo files for translation
• Added theme features
• Added extension contract
• Deprecated: `App\Shared\Helpers\get_private_site_url(string $path = ''): string;`
• Deprecated: `App\Shared\Helpers\get_private_site_upload_url(string $path = ''): string;`

Full Changelog: v1.1.1...v1.2.0