Skip reblogged posts.

• Adds an option to skip reblogged posts and download only original content from the author.
• Improves the download of inlined photos and videos in text posts (e.g. a picture in a answer posts).
• Other minor bugfixes (see the last six commits).

Note: You have to set Download reblogged posts for each old dataset. Simply select all blogs (ctrl-a) and mark the checkbox in the Details view.