Rename example directories to match the source install destination

To match other modules example directory structures we should deploy our
examples in a directory matching the module name, webengine and
webenginewidgets in our case.

qmake uses the relative directory of each example up to the upper "examples"
directory to decide where they will be deployed when running the sources
install target.

Change-Id: I59ce7ff8a30f98fad20064c7eecf72b784f1d275
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>