Adds image and mask features, fixes clippath

This PR:
- Adds image support (Example: /test/pdfs/tutorial.pdf - has both paintnlineImageXObject and paintImageXObject)
- Adds mask support( Example: http://stderr.org/doc/libitext-java-doc/www/examples/Chap0613.pdf)
- Fixes clip (Example: Can be seen in many PDFs. Some clipped elements were not visible due to not applying transform)

To avoid problems with IE and older browsers, let's use PDFJS.createObjectURL (https://github.com/mozilla/pdf.js/blob/master/src/shared/util.js#L1420) here, which accept only plain array. We need to merge/concat all `chunks` into single array.