Create a nicer overview page

[ctron]

Currently the overview page in the console lists all kind of information. Without giving any information what this means.

We should create a nice (visually appealing and informational) page which let's people understand what "endpoint" and "integration" mean.

[rmja]

Related to this: It would be really useful with links to the documentation sections in the book. Something like this:

These are the links in the book:

• https://book.drogue.io/drogue-cloud/dev/user-guide/endpoint-coap.html
• https://book.drogue.io/drogue-cloud/dev/user-guide/endpoint-http.html
• https://book.drogue.io/drogue-cloud/dev/user-guide/endpoint-mqtt.html