Create a bottom panel to show secondary content

[bryanl]

What this PR does / why we need it:

This set of changes creates a bottom panel component to show secondary content. This change is meant to supersede the functionality provided in the SliderView component by introducing the following features:

• Only includes a bottom panel and not the contents of the bottom panel. This reduces coupling and allows the parent component to decide what is shown.
• Allows for resizing the content without using the "ghost" method that was previously employed
• Is designed to live in the same container as other content rather than as an overlay. ie. It will push up content when it is activated.

This change also includes:

• Temporarily makes the collapsed navigation view scrollable.

Special notes for your reviewer:

The panel is included, but it is not activated. To see it working, set isBottomPanelEnabled to true in ContainerComponent and add some content to app-bottom-panel in the view.

[mklanjsek]

I like this, except one thing: IMO collapsed navigation should never be scrollable. Can the slider be positioned inside content-area so the navigation still consumes the whole height of the window?

[mklanjsek]

Love this, but I am seeing following problems when testing it:

• after navigating from one page to another, the bottom panel collapses to its minimized state - I would expect it to stay open,
• the compressed side nav is broken after scrollbar has been added - it's impossible to select any items in flyout menu. The flyout menu shows up briefly, but then disappears after pointer is moved over the scrollbar,
• As commented above, I still think that bottom panel has to be be positioned inside the main pane and left navigation should go all the way to the bottom of the window,

[bryanl]

@mklanjsek

• Yes, the panel will collapse. It's not fully integrated as of this commit, so it is disabled. I have code that'll fix that in a future commit.
• I believe this bug is in the compressed size nav code. The menu isn't updating itself properly, and this will need to be fixed before we enable this new feature.
• I'll move the panel inside, but as noted in Left Navigation redesign #1353, we'll need to a better job with the sidebar menu to make it more usable. What I'm going to do is remove the bottom panel component from the container component for now.