Major update to the theme specification

This update changes the title page and cover page specification to use a common set of attributes in titlepage-theme and coverpage-theme such as titlepage-theme: title-fontsize: 30. All the different themes. For example the academic title page theme is

    titlepage: academic
    titlepage-logo: "logo.png"
    titlepage-theme:
      elements: ["\\headerblock", "\\logoblock", "\\titleblock", "\\authorblock", "\\vfill", "\\dateblock"]
      page-align: "center"
      title-style: "doublelinetight"
      title-fontstyle: ["huge", "bfseries"]
      title-space-after: "1.5cm"
      subtitle-fontstyle: "Large"
      author-style: "two-column"
      affiliation-style: "none"
      author-fontstyle: "textsc"
      affiliation-fontstyle: "large"
      logo-space-after: "2\\baselineskip"
      header-fontstyle: ["textsc", "LARGE"]
      header-space-after: "1.5cm"
      date-fontstyle: "large"