Multiple changes in the plugin build infra

Multiple changes in the plugin build infra

- configure.ac - some plugins are enabled by default
- Plugin .so files are placed into corresponding subdirs
- WITH_PLUGIN_TOOLKIT macro is retired - not needed anymore
- plugins/build-data is removed
- plugin makefiles are not building static libs anymore
- plugin makefiles are not installing header files to /usr/include
  anymore

Change-Id: I55681bd9ce34811f7eb1b2b24d9f0ca42df1cf04
Signed-off-by: Damjan Marion <damarion@cisco.com>