[ADD] base: model `ir.default` to store user-defined defaults

addons/account/models/account.py

addons/account/models/account_config_settings.py

addons/account/models/chart_template.py

addons/http_routing/models/ir_http.py

...small_business/data/l10n_cn_small_business_chart_data.xml

addons/l10n_cn_standard/data/account_chart_template_data.xml

addons/payment/controllers/portal.py

...s/purchase_requisition/data/purchase_requisition_data.xml

addons/website/models/website.py

addons/website_sale_stock/models/website.py

addons/website_sale_stock/models/website_config_settings.py

odoo/addons/base/__manifest__.py

odoo/addons/base/ir/__init__.py

odoo/addons/base/ir/ir_default.py

odoo/addons/base/ir/ir_default_view.xml

odoo/addons/base/res/res_config.py

odoo/addons/base/res/res_lang.py

odoo/addons/base/res/res_users.py

odoo/addons/base/security/base_security.xml

odoo/addons/base/security/ir.model.access.csv