[JENKINS-13995]

Now that the context menu is open only when clicking 'v', the tooltip on model link should
be displayed as soon as the mouse hovers over it.
[JENKINS-13995]

Made the 'v' icon bigger to increase the hit test area, and improved the alignment
logic so that the text and the 'v' icon gets vertically aligned.
Elements passed in are already extended via Prototype
Additional 'inside' class allows pre-allocation of the context menu space
Modifying the breadcrumb context menu so that it also requires clicking 'v'.
Breadcrumb is reworked to show descendants to provide additional navigational shortcuts.

Object that implements ModelObjectWithChildren can expose its children in the breadcrumb.
BUG: z-index of the context menu must be bigger than that of the menu selector
BUG: z-index of the context menu must be bigger than that of the menu selector.

And both values need to be still bigger than the z-index of the top sticker
since the breadcrumb bar is on the top-sticker
improving the sample to cover ModelObjectWithChildren
implemented ModelObjectWithChildren in various model object implementations
adding more ModelObjectWithChildren implementations