Adds MavenPreferencePage and related test. Part of #456
Adds extension point org.jboss.reddeer.junit.before.test. Part of #456
Defines Extension for org.jboss.reddeer.junit.before.test ext. point. Part of #456.

Proceeds these actions prior first test is run:

- closes Welcome Screen
- disables downloading of Maven Repo Indexes on startup
Fixes missing javadoc
Improves performance of o.j.r.junit.before.test extension.point processing. Part of #456

- adds possiblity to decide to run method runBeforeTest() only once for whole test suite
- moves extensions evaluating to RedDeerSuite class
- splits extension to this two classes CloseWelcomeScreenExt and DoNotDownloadMavenIndexesExt
- renamed o.j.r.junit.eclipseext to o.j.t.junit.extension