Provide a colour code for the user

[KitsuneRal]

This is to provide a common colour disambiguation functionality across clients. Ideally, it should be compatible with the Riot's algorithm, so that colours in Riot and QMatrixClient match. And then we'll spec it :-D

[a-andreyev]

will try to help :)
for now it looks like react sdk is using 8 levels gradation to differ username colors:

• sender color calculation
• hashCode function

and android app show other colors %)

[a-andreyev]

provided draft proposal via the wiki
feel free to remove/reject if I'm missing something basic or over-engineering the task 🙂

[KitsuneRal]

Closed by #298.