[Feature Require] Change the title of annotations on one page and Annotate the image in PDF.

1. When annotating a PDF file, **hypothesis get the default PDF name which often is a meaningless string.** I have to download, change the file name, upload to docdrop.org and finnally access to annotation. The redundant operations just for renaming a file seem so silly.
2. When annotating a paper, **images or image-liked things (flowchart or table)** often give more direct and intuitive meanings which are often more worthy to be annotated.