This reverts commit 7436fc7374478de34f25abbd549d80436ac6e303.
Now every plugin has a short, introductory readme tiddler that is shown in the online plugin library.
The user interface needs some refinements but it shows the basic principles. The idea is that the translator would email their modified file, which would then be merged into the core repo (some additional tools will be helpful for this). Fixes #984