Add rotate control

 - displayed when rotation ≠ 0
 - reset rotation on click
Add rotate control to defaults.
Add base control class, to simplify stylesheet
Remove useless test in default controls
Add "origin" option to ol.style.Image
Make Replay API use ol.style.Image "origin"
Make Immediate API use ol.style.Image "origin"
Merge pull request #2040 from elemoine/iconsprite

Ability to use sprites as Icon src
Generate metadata for boolean defines in addition to exportable symbols
Rename generate-symbols.js to generate-info.js

This task generates build related metadata for the library based on doc annotations.  Since it is about more than writing out exportable symbols, it makes sense to have a more general name.
Add description to symbols and defines
Document boolean defines as positive assertions
Merge pull request #2039 from tschaub/defines

Add info on defines to general build metadata.
Merge pull request #2027 from tonio/rotate

Add a rotate control
Use actual circle canvas size
Make check-example.js display console logs from page
Merge pull request #2042 from elemoine/circle

Use correct circle canvas size