Extract "Settings" from redux - part 2: global setting values

The Settings currently use redux for no good reason. Create a context for global settings used across the app:

• Values:
  • sonar.lf.enableGravatar
  • sonar.lf.gravatarServerUrl
  • sonar.analytics.gtm.trackingId
  • sonar.lf.logoUrl
  • sonar.lf.logoWidthPx
  • sonar.dbcleaner.auditHousekeeping
  • sonar.developerAggregatedInfo.disabled
  • Sonar.updatecenter.activate
  • sonar.technicalDebt.ratingGrid