StepDefinitions.addSeriesToCollection(): simplify a step by opening a series from the beginning

[php-coder]

In the StepDefinitions.addSeriesToCollection() method, we open a main page, click on a link with a series, then we do something useful on a page with a series:

mystamps/src/test/java/ru/mystamps/web/tests/StepDefinitions.java

Lines 51 to 59 in f72c87d

	public void addSeriesToCollection() {
	driver.get(Url.SITE);
	driver.findElement(By.linkText("1 item(s)")).click();
	if (driver.findElements(By.id("series-danger")).size() != 0) {
	driver.findElement(By.id("series-danger")).click();
	driver.get(Url.SITE);
	driver.findElement(By.linkText("1 item(s)")).click();
	}
	driver.findElement(By.id("series-success")).click();

While it works, it makes test more fragile because test will fail if we modify a series to, let's say, "2 item(s)"). But the most important things here is performance -- opening the pages is a slow process and we shouldn't do it if we don't really need it.

Let's just open a page with a series (/series/1) -- it's simpler and faster.

Tech debt for f72c87d (#46)

[php-coder]

Won't fix as we're going get rid of Cucumber JVM (#1019).