Add various improvements to scroll Thumbnails into view - comments addressed
Default to a built-in font if an invalid non-embedded font is encountered
Merge pull request #2509 from Snuffleupagus/tweak-thumbnail-scrolling

Add various improvements to scroll Thumbnails into view
Merge pull request #2557 from mduan/issue2391-invalid-font

Default to a built-in font if an invalid non-embedded font is encountered
[PROTOTYPE] Implementation of back/forward navigation in PDFs