Start PZP service on platform initialisation

Jira issue: WP-283

This commit is the first of a series to address this issue.
Here the PZPService is unconditionally started by PlatformInit.
The PZPService in turn starts the PZP itself if the autoStart option
is enabled (which is the default). If the PZP does not auto-start,
it remains controllable via the PZPConfigActivity, which is now
accessible from the Settings option on the WidgetListActivity.

This commit does not yet synchronise with the startup event that
is emitted by the PZP, so it indicates the started state as soon
as the PZP isolate runs.

Further, this does not yet attempt to restart the PZP if it exits.
Merge pull request #517 from paddybyers/android-pzp-autostart

Start PZP service on platform initialisation