Group-income-simple: Create a welcome page for new members of a group

[mmbotelho]

Problem

At the moment, we still don't have a substitute for the welcome page - the first page new members see when they join a new group. The current version looks like this:

Solution

Update this page.

[mmbotelho]

Design for this task discussed and approved during the hackathon.

Figma link
https://www.figma.com/file/mxGadAHfkWH6qApebQvcdN/Group-Income-2.0?node-id=2371%3A0

[taoeffect]

NOTE: it is good @mmbotelho designed it this way, since showing who the existing group members are in a group (to someone not-yet-in-the-group) might turn out to be a challenge, since most group information is encrypted.