Updated matchers (renaming, documentation, refactoring) #482

- Documentation:
Added verbose documentation to all classes in package
org.jboss.reddeer.swt.matcher

- Matchers:
Implemented methods describeTo(Description) and toString()
Added NullPointerException check into constructors

TextMatcher renamed to WithTextMatcher
StyleMatcher renamed to WithStyleMatcher
RegexMatcher renamed to WithRegexMatcher
WithMnemonicMatcher renamed to WithMnemonicTextMatcher
LabelMatcher renamed to WithLabelMatcher

Added constructor with Matcher<String> to WithTextMatcher
Added constructor with Matcher<String> to WithMnemonicTextMatcher

- Comfortable matchers construction:
TextMatchers renamed to WithTextMatchers
RegexMatchers renamed to WithRegexMatchers
WithMnemonicMatchers renamed to WithMnemonicTextMatchers

- Architecture:
ObjectToStringMatcherDecorator replaced by AbstractWidgetWithText-
Matcher. The idea, of having abstract class for extracting text from
widgets, was kept. However, AbstractWidgetWithTextMatcher allows to
specify evaluating of extracted text from widget.