Convert event.device from NSDictionary to a structured class

[fractalwrench]

Goal

Converts event.device from an NSDictionary to a structured class where each field is represented as a property.

BugsnagDevice is used for sessions, and contains stateless properties that do not change over the lifecycle of an application. BugsnagDeviceWithState extends this class and is used for events, and contains stateful properties that change for each error - e.g. freeDisk.

Changeset

• Added BugsnagDevice and BugsnagDeviceWithState classes with properties for each field in the spec
• Altered BugsnagEvent to use readonly BugsnagDeviceWithState for event.device
• Refactored BSGParseDevice and BSGParseDeviceWithState methods into new BugsnagDevice classes, so that they can parse a KSCrash report and populate their fields
• Extracted JSON serialization into BugsnagDevice/WithState from BugsnagEvent
• Moved surplus device metadata fields into event.metadata

Tests

• Added unit test to verify that BugsnagDevice and BugsnagDeviceWithState populate correctly, and that they serialize JSON correctly
• Updated existing test coverage
• Ran example app and verified that device data is sent to the dashboard for an event

[robinmacharg]

Looks good in the main. A couple of simplifying refactorings that seem to make sense in the context of the move to structured device info have been suggested; probably worth scanning all the comments once over. One outstanding question I have is over what looks like the removal of the wordSize field from session device payloads. Understanding that decision would be useful.

[robinmacharg]

Thanks for the changes, looks good!