feat: add install handler and related logic

- Mako is now a core dependency
- therefore no more 'email' extra
- add `get_install_handler()` method for app handler
- add `render_mako_template()` method for app handler
- add `resource_path()` method for app handler
- install handler thus far can:
  - confirm db connection
  - make appdir plus config/scripts:
    - wutta.conf
    - web.conf
    - upgrade.sh
  - upgrade db schema to create tables
  - from there web app can run, create admin user
- quick start docs now describe "generated code" option

docs/glossary.rst

@@ -145,6 +145,12 @@ Glossary
      Similar to a "plugin" concept but only *one* handler may be used
      for a given purpose.  See also :doc:`narr/handlers/index`.
 
+   install handler
+      The :term:`handler` responsible for installing a new instance of
+      the :term:`app`.
+
+      Default is :class:`~wuttjamaican.install.InstallHandler`.
+
    package
      Generally refers to a proper Python package, i.e. a collection of
      modules etc. which is installed via ``pip``.  See also