Migrate all widget doc to Sphinx

[adube]

problem

Actually, the widget documentation is scattered all over the place. Some are in Sphinx, some are in Natural doc and some are still in the ./docs/widgetdoc.txt file.

solution

• Migrate all widget doc to sphinx
  
• Purge the old stuff
  

[adube]

Since this work involves a lot of changes that won't have any effect on the code directly, I would go with lots of commits instead of creating patches.

[adube]

r746

All editfeatures widgets are now migrated to Sphinx. More work should be done with them (more config samples, more samples, etc.) but that's out of the tasks of this ticket.

[adube]

r753

!FeaturePanel_Form widget documentation moved to Sphinx. Again, more work needs to be done (more samples, more config samples) but again this is out of this ticket.

[adube]

r754

Toolbar
GeoExtToolbar

[adube]

r755, QuickZoom

[adube]

r756, scale, measuretool, popup, queryonclick, getmouseposition, mouseposition

[adube]

r757, merge, split

[adube]

r758, mapfishrecenter, mapfishlayertree, resultextgrid, queryonclick, featurepanel_selector

[adube]

r759 zoomslider, legendpanel

[adube]

r760, old documentation is now purged.

Migration completed