Update closure-util
Add error handler

If the server fails to start, display error message and exit.  Typically this is due to the address being in use.
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 pull request #1507 from tschaub/update-closure-util

Update closure util.
Fix ol.BrowserFeature.HAS_WEBGL test in side-by-side example
Merge pull request #1523 from fredj/side-by-side

Fix ol.BrowserFeature.HAS_WEBGL test in side-by-side example