Structured logging on clients (opentracing compatible)

[BillCarsonFr]

First step for: #31

Goal
Improve the logging in general
Switch to structured logging and a common output format for those logs (e.g. opentracing compatible)
Improve the experience when going through rageshakes, if our shakes are opentracing compatible we could use jaeger to inspect/search through them

• Define the common output format (opentracing compatible) #40
• Implement on web
• Implement on iOS
• Implement on Android

[richvdh]

Duplicate of https://github.com/element-hq/crypto-internal/issues/132 (which has been closed as "not planned")