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.
Instead of throwing a 500 error if a user enters an invalid name,
display the same text box as if the user had entered the wrong
password.
NOTE: An invalid username now returns much quicker than an invalid
password. Consider adding an arbitrary sleep in the future if we
care about masking which was invalid.
Let the server handle the state token instead of the connector. As a
result it can throw out bad requests earlier. It can also use that
token to determine which connector was used to generate the request
allowing all connectors to share the same callback URL.
Callbacks now all look like:
https://dex.example.com/callback
Instead of:
https://dex.example.com/callback/(connector id)
Even when multiple connectors are being used.
