Clients::Studio: show properties in factory details window

    * src/clients/studio/factoryinfowindow.cpp:
    * src/clients/studio/factoryinfowindow.h: feed model of properties
      tree view by property name and property description.
    * src/clients/studio/ui/plugininfo.glade: added tree view to a factory
      info window, which contains element's properites.
Clients::Studio: added filtering to a plugins inspector

    * src/clients/studio/mainwindow.cpp: load searchbox pointer to a
      inspector object.
    * src/clients/studio/plugininspector.{cpp|h}: implemented search
      filter, added it to a treeview with plugins. Implemented resursive
      search, to avoid hidding found elements.
    * src/clients/studio/ui/mainwindow.glade: added searchentry.
Clients::Studio: added classes for visual representation elements

    * configure.ac: added goocanvasmm-2.0 dependency.
    * src/clients/studio/Makefile.am: added to a build files with classes
      which represents visual blocks.
    * src/clients/studio/elementitem.{cpp|h}: class representing gstreamer
      element.
    * src/clients/studio/paditem.{cpp|h}: class representing gstreamer
      pads.
    * src/clients/studio/mainwindow.{cpp|h}: added workspace (canvas) to
      a main window.
    * src/clients/studio/ui/mainwindow.glade: added scrolled window
      for goocanvas element.
Clients::Studio: fixed drawing pads

    * src/clients/studio/elementitem.{h|cpp}: added get_width, get_height
      methods, drawing pads according to an element width.
    * src/clients/studio/mainwindow.cpp: minor change (for test purpose).
    * src/clients/studio/paditem.{cpp|h}: added get_width and get_height
      methods.
Clients::Studio: segfault fixed

    * src/core/propertycontainer.{cpp|h}: changed interface of
      PropertyContainer constructor, passing argument by copy, not by
      reference. RefPtr is lightweight object, so copy isn't so
      resource-consuming, and it allows me to simplify this method's call.