Discuss security for client applications

[Tschakki]

Description

Discuss security of blockchain client applications, and how to keep the user data safe. Describe advantages and disadvantages of the different approaches like metamask, a web ui or a standalone application (what other approaches do exist?)

Motivation

As this topic is very important for every sidechain developer, we should provide best practices, compare different approaches, and warn about possible security risks if best practises are not followed.

Additional information

Maybe wait for v6, and secure signing?