testing some mapcss text rendering approach
add mapbbcode licence info
make only text-part of (short) PopupIcons clickable

I see that icons must have a fixed width in order to center them. But it resulted in the whole area being clickable (even the transparent areas right and left of the text). This behaviour is especially confusing if texts are short, but right next to each other.

This uses [pointer-events](http://caniuse.com/pointer-events) to make the transparent areas right and left of PopupIcons non-clickable. And it doesn't harm older browsers.
Merge branch 'master' into text-markers
still show circle markers even when text markers are shown
(hacky) support for "symbol-shape: none;" (MapCSS)

usefull if one only wants to print a text label and nothing else
make labeling work also for (multi)polygons and linestrings*

* not so well suited for ways right now, as the center of the bounding
  box is usually not such a good point to put a label there.
better label placement for linestrings
update mapbbcode library, add a little opacity to text markers
add attribution to MapBBCode library