dev branch: add SQL storage implementation

This change adds support for SQLite3, and Postgres.

Currently, whether or not a user has authenticated themselves through
a connector is indicated by a pointer being nil or non-nil. Instead
add an explicit flag that marks this.

dev branch: add TODO file

dev-branch: generate string literals instead of escaped strings

When compiling the default templates into the source code, use
string literals instead of escaped strings to reduce merge
conflicts.

dev branch: port templates from master branch

Add a small program to iterate over the templates directory and
generate a go map of name to file data. This is so we can compile
these templates into the dex binary instead of requiring files on
disk.

Also add a Makefile rule to do this automatically.

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.

dev branch: set response types supported in discovery based on server config

While the issue tracker is being used for the master branch, add a
TODO file to record work to do on this branch. Issues are currently
unprioritized and do not indicate requirements for any particular
milestone.

dev branch: support the implicit flow

dev branch: fix oauth2 values and remove unused code

dev branch: run server tests at a non-root URL

As we've seen on master it's very easy mistakenly make changes that
assume root URL paths. Run server integration tests at a non-root
issuer URL to prevent this.

dev branch: enable travis testing