Remove Font Awesome

Everything that we need (icon-arrow-left, icon-arrow-right, icon-plus,
icon-minus, icon-download and icon-flag) is already provided by Bootstrap.
Make setValues consistent with repeated calls to set
Safer feature constructor

Calling setValues now behaves like calling set (closes #1672)
Merge pull request #1728 from tschaub/set-values

Make setValues behave like multiple calls to set.
Merge pull request #1727 from fredj/drop-fontawesome

Remove Font Awesome
Dispatch 'render' event in renderer.canvas.VectorLayer

The context property of the event only contains the vector rendering.
Add ol.layer.Heatmap class and example