simplify telemetry implementation

[jrieken]

Today we have an interface that describes the contract of telemetry (ITelemetryService) which is OK. The bad thing is that there many implementations of that interface (AbstractTS, MainTS, ElectronTS, AbstractRemoteTS, WorkerTS, ExtHostTS, NullTS, MockTS, TestTS) which have led to leakage and duplication of events. I believe this problem should be solved with less code and abstraction

[jrieken]

new structure is like this:

ITelemetryService implemented by:

• NullTelemetryService used in tests et al
• TelemetryService implements a full telemetry service
• ElectronTelemetryService extends above and adds better machine/session identifiers
• RemoteTelemetryService a proxy in workers/extension host

[jrieken]

fyi @aeschli