Linker improvements

[KockaAdmiralac]

• Make the linker not throw an error when linking to a nonexistent wiki, probably by checking whether it exists before continuing

  Twinkle/src/plugins/linker/index.js

  Line 171 in 8ffe571

  const wiki = await this.getWiki(message.guild);

• Make the linker use buttons instead of reactions for deleting messages
• Make the linker support vanilla MediaWiki wikis better? (I can work on this one)