yoda: Classify options according to "for"-s (v2)

If a group has less then three options, it will be merged into a more
general group.

A group description is generated accoding with following rules:
"action = restore" -> "For restore action"
"command = mount"  -> "For mount command"

v2: add section "Generic", fix generating group description

Signed-off-by: Andrey Vagin <avagin@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@sacred.ru>