Fix #383: Navigation menu titles can't be set in BladeMatter

[caendesilva]

This is caused in FindsNavigationDataForPage.php where the front matter is only read for Markdown pages.

if ($this->page instanceof AbstractMarkdownPage) {
    if ($this->page->matter('navigation.title') !== null) {
        return $this->page->matter('navigation.title');
    }

    if ($this->page->matter('title') !== null) {
        return $this->page->matter('title');
    }
}