Adjust overview page
Adjust overview page

* Make introduction very small instead of huge wall of text
* Move screenshot of seahorse editor to the top of the page
* Rework wall-of-text with features into simple to comprehend list
* Rework old introduction wall of text into 'Vision' paragraph
* Add learn more paragraph

Change-Id: I253a8ed61ff5ea2f36a1f58a99fbcffe7fddf858

deepsense-io/seahorse-workflow-executor,deepsense-io/seahorse-workflow-executor,deepsense-io/seahorse-workflow-executor,deepsense-io/seahorse-workflow-executor