Gui: added GtSlideShow class (to view multiple images), and classes for joinable interfaces/display of lists

Squashed commit of the following:

commit b24355ee2ef49c41fce0b5de696da72640aa83e4
Author: Nicola Vigano <nicola.vigano@esrf.fr>
Date:   Tue Aug 7 01:18:53 2012 +0200

    Gui: GtSlideShow: added better selection of images (by index and list)

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

commit 7a04a43256ad45d4c385ed9c70aa1ff0f8773517
Author: Nicola Vigano <nicola.vigano@esrf.fr>
Date:   Tue Jul 31 20:14:10 2012 +0200

    GtSlideShow: added initial simple class to browse a folder content

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

commit 260ac1d304a2253afb4e5d4d3d8fdb7a86402066
Author: Nicola Vigano <nicola.vigano@esrf.fr>
Date:   Mon Aug 6 19:42:20 2012 +0200

    Gui: added list selector, based on joinable GUIs.

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

commit 0c400c19021df639de402e1c5b95519f9c15c8da
Author: Nicola Vigano <nicola.vigano@esrf.fr>
Date:   Mon Aug 6 19:41:36 2012 +0200

    Gui: added join-able GUI object (to act as a function that returns a value)

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

git-svn-id: https://svn.code.sf.net/p/dct/code/trunk@683 4c865b51-4357-4376-afb4-474e03ccb993