Implement getPage with page id instead of key.

findPage already supports it.

This fixes NPE with foreign languages, where key stored (english)
was different than the actual one (translated).

Change-Id: Iafd81a39974b969046c5c485d7d8732695c952f1

Conflicts:
	src/com/mokee/setupwizard/ui/SetupWizardActivity.java