When we fail to download textures or geometry, retry after steadily increasing
delays.  Closes #1471.
Merge branch 'master' of https://github.com/worklist/hifi into retryagain
Merge pull request #1512 from ey6es/retryagain

After failing to download textures or geometry, retry again after increasing delays.
Merge branch 'master' of git://github.com/worklist/hifi into windows_build