Merge pull request #795 from fredj/pan_actionbutton

Right click pan
Don't attempt to constrain values in setters
Make ol.control.Control extends ol.Object
Basic support for text symbolizers

This adds basic label rendering for points and polygons to the
canvas renderer, and a text symbolizer to the style package.
Fixing merge errors from unmerging #404
Use 'text' instead of 'name' for the label text
Changing renderLabels_ method name to renderText_
Prevent buttons from setting out-of-range brightness/contrast/saturation values
Stop buttons from moving so much when changing values
The map now has a collection of controls
Add 'units' property to ol.control.ScaleLine
Add addControl and removeControl methods to ol.Map
Proper handling of defaults
Adding TODOs
Updating example to use new properties
Merge pull request #770 from ahocevar/text-symbolizer

Basic support for text symbolizers. r=@bartvde,@tschaub
Do not call setMap(null) if control not in map
Add 'projection' and 'coordinateFormat' to ol.control.MousePosition
Meaningful variable names
Merge pull request #798 from twpayne/fix-layer-setters

Don't attempt to constrain values in setters