Order feature page by message, solution, or subject

In https://gitlab.com/gitlab-com/www-gitlab-com/issues/1334 we had to remove all the ordering from the features page.

The old features page had groupings like:

1. Powerful features for modern software development. Tightly integrated into one platform.
2. Consolidate your source code. Wrangle your projects into one easy-to-manage tool.
3. Track and manage releases. Ease the collaboration process with a single tool to track issues and monitor progress on your releases.
4. Increase code quality. Code collaboratively and trust your code review with fast branching and powerful diff tools.
5. Deploy with confidence. Test, build, and deploy your code.
6. Follow changes and progress. Keep track of the progress and activity on your projects.

Solutions consists of phases solutions and quality solutions. Features will now be grouped by solution. Every feature will have exactly one solution associated with it.

Phase solutions are:

1. Chat (Mattermost)
2. Define (Issue tracker)
3. Plan (Issue board, Portfolio Management)
4. Create (Auto web terminal, Auto web IDE, Auto Start)
5. Review (Auto CI, Auto Code Quality, Auto Review Apps, Au)
6. Release (Auto build, Auto Correlation, Auto Rollout, etc.)
7. Monitor (Prometheus, Auto Metrics, Auto Scale)

Quality solutions include the following categories:

• Scalability
• Availability
• Compliance
• Security
• Services (services we provide)
• Wiki
• Pages
• Service desk (our service desk feature)
• Innersourcing
• Integration
• Open core (anything related to self hosting)
• Efficiency (ChatOps, cycle time analytics, todo's, everything that makes people more efficient)
• GitLab.com
• Missing (stuff that we don't have)
• Importing

On the new features page the format is:

1. Solution header
2. Description that links to the solution page
3. Features, each one has a CE EE EEP tag like on https://about.gitlab.com/2017/05/22/gitlab-9-2-released/

If you want to it ordered per edition there already is /products to see that.

Each top level solution have an auto-generated page such as /solution/plan too.

Have a solutions.yml file that lists solutions. Each solution has a header (main item), a description, a blob of text, and 0 to many customer case studies. Each solution has 0 to many solutions that are related to it.

In features.yml file link every feature to exactly one solution. If they are not linked to a solution they can't be shown on the features page.

The solution page /solutions will have:

1. Solution header
2. Blob of text
3. Link to the individual page

On an individual solution page /solutions/compliance the format is:

1. Solution header
2. Blob of text
3. Case studies
4. Features
5. Related solutions