bugfix: negative push duration time in 802.1q

If the push process was interrupted, the "schedule" portlet was
displaying negative push duration. Also, all ages were displayed in
hours. Now formatAge function is used.

getVLANSwitchInfo: row format is changed. The following keys were
removed: last_push_lasted, last_change_age, last_change_age_seconds,
last_error_age, last_error_age_seconds, last_push_age.
The following keys changed their format from DB-formatted datetime to
integer UNIX timestemp: last_change, last_push_finished,last_error_ts.
The last_push_started key was added.

detectVLANSwitchQueue: calculate change_age amd error_age
renderObject8021QSyncSchedule: use datetimestrFromTimestamp and formatAge
renderDeployQueue: idem
config var DATETIME_FORMAT description changed

date() was replaced by strftime() in description