With this commit JS console logs can optionally be sent to the RTCstats server
for storage and processing.

The functionality is off by default and can be enabled by setting to `true` the
config.js option

    config.analytics.rtcstatsStoreLogs: false // off by default

Obviously, if rtcstats is disabled/not configured nothing will be sent to the
rtcstats backend, even if this setting is set to `true`.

This commit also adds a config.js option that can be used to disable sending the
logs back to callstats:

    config.callstatsStoreLogs: true // on by default

Obviously, if callstats is disabled nothing would be sent in the first place,
but if callstats is enabled and this new configuration parameter is set to
`false`, then callstats will be kept active but no logs will be sent to
callstats.