Adds 'Condition:CanWither' flag to numerous skills and supports

[krryan]

Description of the problem being solved:

The “# of Wither Stacks” config was not enabled by Chaos Bolt, His Foul Emergence, Withering Presence, Withering Touch, Wither Away, or The Right Hand of Darkness.

Steps taken to verify a working solution:

• Added each skill listed above one by one (without the others), to ensure the “# of Wither Stacks” config appeared as expected in each case.

Link to a build that showcases this PR:

https://pobb.in/RRWhH42PJV3X
(Not that there’s much point, just add any of the skills or take any of the nodes listed here.)

Before screenshot:

After screenshot:

[krryan]

I attempted to add unit tests for this, but couldn’t figure out how to test that the config was shown. I was using

	it("Test Wither stack config with Chaos Bolt", function()
		build.skillsTab:PasteSocketGroup("Chaos Bolt 1/0  1\n")

		assert.is_true(build.configTab.varControls.multiplierWitheredStackCount.shown())
	end)

but I think I need to run something in between these two to get the .shown() to update. I tried configTab:BuildModList() and configTab:UpdateControls(), but those did not work. I realize there aren’t a ton of unit tests here, and this is a pretty simple thing that maybe doesn’t need them, but thought the commentary might be useful for maintainers as something to think about if you’d like to see more unit tests.