Add Gel and sort Managed Data Services section.

[Leftium]

This PR has two commits:

1. Add Gel.
2. Alphabetically sort Managed Data Services.

Requirements

• [x] This is Software as a Service not self hosted
• [x] It has a free tier not just a free trial
• [x] Pricing information is clearly visible without signup or phone calls
• [x] The submission mentions what is free
• [x] The submission is not already present in the list
• [x] The service has contact details of those running it and a privacy policy