Migrate to the latest version of Flexdock

The version of Flexdock we use is 0.5.1 while the latest version is 1.2.4 (http://forge.scilab.org/index.php/p/flexdock/). The API has changed significantly, therefore the code needs to be updated. Also the way the layout is stored is changed, which may cause some problems.

Note: FlexDock is upgraded to 1.2.4, but the save-load feature is not reliable.
As FlexDock is not supported anymore, the best option is to migrate to DockingFrames (http://dock.javaforge.com/doc.html).