Replace OMERO downloads page template using Gus' tokenized page

OMERO downloads page generation now directly substitutes token on an HTML
page rather than generating an intermediate Markdown page.
Use copyright symbol
Drop pelican step from OMERO downloads page generation
Copy images folder to content
Drop unwanted _URL at the end of token
Add tokens and logic to compute artifacts size
Fix symbol in size computation
Comment tag sha1 computation (not used in current downloads page version)
Fix Ice 3.4 server size
Fix flake8 and removed tmpl.txt
Replace wording for checksum download link
Fix checksum hyperlinks and add hyperlink to the artifact names
Compute short version of checksums
Reimplement logic to compute tag link and add button in downloads page
Fix flake8 warnings
Fix TAG_URL
Refactor tag lookup logic and displayu tag URL instead of commit URL
Remove base artifact name hyperlinks
Fix human size generation (using powers of 10 instead of 1024)
Merge pull request #27 from sbesson/omero_downloads_page

Omero downloads page