Add file logger RN example

[dangeross]

This PR adds to the React Native example additional code to log to file SDK log entries and events, which can then be shared via email.

Added to the example are dependencies:

• react-native-file-logger
• react-navigation

To configure the file logger, we disable capturing console logs by default and set the max number of log files to 5 (5 days of logs). You can additionally set the maximumFileSize to limit the file size:

FileLogger.configure({
    captureConsole: false,
    maximumNumberOfFiles: 5
})

We wrap the capturing of log entries to a utility class Log which can log both to console and optionally to file:

import { Log } from "../utils/logging"

const log = new Log("ExampleApp")
log.debug(`Log a debug log entry to file`, true)

We update the SDK logHandler in the HomeScreen to use the Log class to capture logs:

    const logHandler = (logEntry) => {
        switch (logEntry.level) {
            case "ERROR":
                log.error(`[ERROR]: ${logEntry.line}`, true)
                break
            case "TRACE":
                // Only log to file when in DEBUG mode
                log.debug(`[TRACE]: ${logEntry.line}`, DEBUG)
                break
            default:
                log.debug(`[${logEntry.level}]: ${logEntry.line}`, true)
                break
        }
    }

And finally add a button to trigger sending the log file via email:

        try {
            await FileLogger.sendLogFilesByEmail({
                subject: "Logs",
                body: `OS: ${Platform.OS} - ${Platform.Version}\n\n` + JSON.stringify(nodeInfo, null, 2)
            })
        } catch (e) {
            log.error(JSON.stringify(e))
        }

[roeierez]

LGTM