move kcron kcm docbook to subdir kcontrol, proofread + update date/releaseinfo

the kcron kcm docbook was installed to subdir kcontrol/kcron, but the translated docbooks to subdir kcron,
therefore the language docbooks are not found in kf5 khelpcenter and only the english docbook is displayed

To fix this:
move kcron kcm docbook to subdir kcontrol, consistent to dir layout in kde4 and as dir layout kdeutils/kdf
proofread + update date/releaseinfo
REVIEW:129808