Revisiting the interwiki map

Created by: lahwaacz

The current interwiki map is in desperate need of revision:

1. It is based on upstream's interwiki.list, which is obviously intended only as an example. Most of the entries will never be used on ArchWiki due to different target audience.
2. It contains entries for unaccessible sites (for example http://gentoo-wiki.com/) or they are redirected to an unrelated site.
3. It contains invalid entries. As per upstream documentation, all interwiki prefixes must be strictly lowercase, but the table contains many CamelCase prefixes. I've tested it in the sandbox and using them indeed creates a normal wiki link, not an interwiki link.
4. Some entries are totally broken with respect to the interwiki functionality. For example http://www.google.com/ has no chance of functioning properly as an interwiki because spaces are not supported in the interwiki link, the parser always puts an underscore in its place (same for %20).
5. It does not contain many frequently used wikis or shortcuts.

I've tried to solve the above issues by creating a new SQL script in maintenance/arch-interwiki.sql, which should be applied on the ArchWiki database. In order to clean up the junk, the table is first cleared and the wanted entries are then added. I can confirm that none of the removed or added prefixes are currently used on both wiki.archlinux.org and wiki.archlinux.de, so the current content should not be affected.

I've used the upstream's maintenance/interwiki.sql script as the base for my changes, but it is only a subset of the actual interwiki map. Nevertheless, the complement is made up of either invalid entries (see 2. and 3. above) or completely useless entries (see 1.) that would be removed either way. I hope that not tracking them is not a problem.

This will also solve FS#45157.

If there are some other ideas for entries that should be added, I can update the pull request.