Add link to Google's unpacked extension installer help
Fixed wrong filename for ZIPs and CBZs

Single image names are still wrong.
Filename and crash fixes

- Single image downloads get correct filenames now
- Single image PNG downloads do not cause a crash anymore
- Updated README to explain the new extension origin policy for Chrome
for Windows
Merge branch 'downloadFilenameFix' into fastDownload

Conflicts:
	source/bgPage.js
	source/manifest.json
Resolved merge conflicts