Add SplitPanel component

[feathergrass]

It would be nice to have methods: Sidebar.setOpen(Boolean), Sidebar.isDisplayed().

Now I use the next realization of the Sidebar.

public class Sidebar extends Composite<Sidebar> {
    public void open() {
        sleep(300);
        if ($(By.className("c-splitpanel-dock-button-left")).isDisplayed()) return;
        SelenideElement splitpanelButtonRight = $(By.className("c-splitpanel-dock-button-right"));
        splitpanelButtonRight.shouldBe(Condition.visible);

        while (splitpanelButtonRight.isDisplayed()) {
            splitpanelButtonRight.click();
            $(By.className("c-splitpanel-dock-button-left")).shouldBe(Condition.visible);
            splitpanelButtonRight = $(By.className("c-splitpanel-dock-button-right"));
        }
    }
}

Known issue: Sometimes it opens search folder.

[dtsaryov]

Not a generic case.

[natfirst]

@dtsaryov we should implement the SplitPanel component as an ability to work with it on the main screen:

• check, if it is visible
• open and close it