Handle case where resource has no imagery providers
Merge pull request #1510 from tschaub/bing-providers

Handle case where Bing resource has no imagery providers.
Add optional URL for logos
Add ol3Logo option to ol.Map
Add 32x32 pixel logo image
Add optimized 32x32 pixel logo
Use compressed logo URL
Merge pull request #1511 from twpayne/powered-by-ol3

Add ol3 logo by default
Merge remote-tracking branch 'openlayers/master' into vector-api