Adapting the web site to the GUI

(I had posted this to slack channel, but let's discuss it here instead for better archiving.)

Here's how we could –temporarily– reorganize the website navigation to include basic GUI documentation:

On the Home page, we can add direct download links to the app.

As for the site map:
- Getting started _(new heading, but not a page)_
- Why Ace? _(no changes)_
- Ace app _(a very brief intro of the app, linking to the "installation" page)_
- Ace command line tool _(a very brief into of the CLI, linking to the "installation" page)_
- Ace app _(new heading, but not a page)_
- Installation _(new page documenting how to get and run the installer)_
- Using the Ace app _(new page documenting how to get started with the GUI)_
- Ace command line _(new heading, but not a page)_
- Installation _(use the page currently under the "Getting Started" section)_
- Running the Ace command _(use the page currently under the "Getting Started" section)_
- Options _(copy of the page "Command line interface" currently under "Reference")_
- Configuration _(copy of the page currently under "Reference")_
- Logging _(copy of the page currently under "Reference")_
- HTTP API _(copy of the page currently under "Reference")_
- Ace Report
- Using the Report _(adapted from the page "HTML Report" in the current "Reference" section)_
- Exporting to JSON _(new content combined with "JSON Report" in the current "Reference" section)_
- _… the following sections are kept unchanged…_

@danielweck wdyt?