Improve links on package page.

Don't show the full links, instead just show "Website", "Issue tracker" etc and link to the relevant place.

Also replaced "For full details and additional technical information, see this application's page on the F-Droid wiki." with "Technical info" and linked it directly to the wiki.

Old version | New version (don't worry about the broken "GPL" link, this is due to metadaata in the GP repo.