add PLUGIN_CLASS_NAME declarations to plugin projects

needed for automatic static linking (and later deployment).
the gesture plugins are excluded from the automation based on the
assumption that they are usually not needed.
the example and the test plugin are also excluded for obvious reasons.

Change-Id: I7645aa0daf216ce430989e13d4380dbe6dd2bbd1
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>