harmonize all plugins docs

original issue #1012
 
Add a configuration section that lists all options for each plugin.
List options in alphabetic order.
Mention the default value for each option.
Use same sentences to describe concepts common to different plugins eg 'auto' option, install description
We should probably be consistent about whether there's a colon between the option name and the rest of the description. Either way is fine, but let's pick one.