Step 1 for utfgrid mouseover

NOTE:  had to modify OpenLayers UTFGrid control line 227
changed from var candidates = this.layers || this.map.layers;
to var candidates = this.map.layers;
At present the mouseover event creates an un-styled block of text.
Next steps will involve utilizing the same popup feature used by vector
mouseover events….
Step 2 for utfgrid mouseover

refactoring vector mouseover functions to be usable by utfgrid mouseover
Step 3a for utfgrid mouseover

close, but not quite - still working out the interplay between vector
and utf popups…
Step 3b for utfgrid mouseover

vector and utf mouseover events now playing nice with each other (only
showing one at a time).  remaining problem is moving off utfgrid
mouseover onto vector mouseover does not re-trigger the vector
mouseover event…committing code that has a failed attempt commented out
(just for archiving purposes)
Step 4 for utfgrid mouseover (close enough for now)

Factoring out mouseover and click events from map.js to their own files
Merge branch 'mouseover' into next-release
addressing a problem with attribute overlays for vector layers

resulting from the utfgrid mouseover merge.
These overlays were not showing up for subsequent click events
(clicking on a layer the first time would provide an overlay,
additional clicks would not)