Http Server: Add redirect exception

This adds a redirect execption that would allow a handler to return a
301 redirect with a given URL.

Now if a handler wishes to redirct the to new_url it can call:
throw redirect_exception(new_url);

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Http Server: Adds a force path option to file_handler

When file_handler return an html file, it sometimes relay that the path
to it would end with a slash, in those cases, when it is called without
the slash, the desire behaviour would be to redirect the request to the
same url with a slash.

This adds an optional parameter to the file_handler constructor, to
force the path to end with a slash.

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Http Server: Setting the GUI as the root URL

This moves the GUI to be the root path, so a call to:
localhost:8000/ will be redirect to localhost:8000/dashboard and will
display the GUI instead of the Swagger-ui

The swagger-ui was moved to:
localhost:8000/api-gui

Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>