Stenmark 0.7.0

• Use mk@singular.de for the translator credit too
• Credit the German translation
• Track the editor source, and add the themes.json generator
• Bring the 0.7 release notes up to date
• Move the window size into Preferences
• Stop tracking node_modules
• Offer 48 editor themes, with a preview beside the picker
• Give Preferences a window of its own
• Start editing where you were reading
• Don't let a pending dead key swallow control keys
• Write the release notes for 0.7
• Give the search scope its own msgids
• Add screenshots to the AppStream metadata
• Move screenshots to data/screenshots for AppStream
• Update PKGBUILD checksums for v0.6.1