[2/3] cleanup static reference

[omochi]

• Remove static shared things in ViewController

• Define new singleton class NumswPlayground. This is root component for static objects. So it has a RenderViewController.

• Change book initialize code _setupRender to NumswPlayground.initialize()

• Cleanup global function style API implementation example:

public func addLine(
    x: [Double], y: [Double])
{
    NumswPlayground.shared.addLine(x: x, y: y)
}

public func addLine2(
    x: [Double], y: [Double],
    x2: [Double], y2: [Double])
{
    NumswPlayground.shared.addLine2(x: x, y: y,
                                    x2: x2, y2: y2)
}

they are simply transfer invocation to singleton instance method.

• To make sources as many as possible testable on iPad sandbox app, split file for codes which need to import PlaygroundSupport into NumswPlayground_Playground.swift and all others can be compiled within iPad app target.

[omochi]

This PR is orthogonal with #9 semantically. But it may conflict around RenderViewController. If to be so i will fix it.

[sonsongithub]

Is this commit UITableViewController version?

[omochi]

@sonsongithub Yes, but I found a new bug with UITableViewController version...

[omochi]

Oh, this includes #9 commits. I will fix this.

[omochi]

I switch back to ScrollView. It is easy to switch back TableView now.

[omochi]

now this PR includes #9

its ready to merge