Replace Item, Spec and Plugin Toolbars

[ptsavol]

I propose we replace the Generic Items, Specifications, and PlugIn Toolbars with simple lists in a single dockwidget. The problem with the current Toolbars is that they take up a lot of space and when there are multiple plugins installed I'm struggling to find a good place for them. Another problem is the Title widget in each Toolbar. Qt does not support adding a title to toolbars and I could not find, with a quick search, a good example on any other app using a title in a toolbar. This probably means that a Toolbar is not the right widget for the job.

There will be one Toolbar left, which will contain the play and stop buttons and a place for an animation or a progress bar that shows the progress of the execution. The line edit in the pic below is a placeholder for this.

Here's a teaser to clarify what I wanted to do. Clicking the yellow items collapses/expands the tree so there's plenty of room for bigger projects as well.