This PR reworks the web layout so static files can be provided and
a "themes" directory to allow a certain degree of control over logos,
styles, etc.
This PR does NOT add general support for frontend customization,
only enough to allow us to start exploring theming internally.
The dex binary also must now be run from the root directory since
templates are no longer "compiled into" the binary.
The docker image has been updated with frontend assets.
Bcrypt'd hashes have "$" characters in them. This means that #667
(accepting actually bcrypted values) combined with #627 (expanding
config with environment variables) broke the example config.
For now, allow storages and connectors to expand their configs from
the environment, but don't do this anywhere else.
Allow users to define config values which are read form environemnt
variables. Helpful for sensitive variables such as OAuth2 client IDs
or LDAP credentials.
Since we don't have a good strategy which takes a username and password
add a mock connector which implementes PasswordConnector so we can
develop the frontend screens.
