battery: rename battery.online as charger_connected

battery: rename battery.online as charger_connected

 The charger_connected has changed to have only a value of 0 or 1,
which corresponds to charger disconnected/connected. At before, the
variable can have any integer other than 0 or 1, which implied which
type of charger had been connected. Instead of those integers, the
power_source_s or vconf can be utilized for charger type.
 The vconf, VCONFKEY_SYSMAN_CHARGER_TYPE, which was exclusive for MCD
product profile, has changed to have a one of the value belows, and it
will be changed according to battery.power_source_s.
    0 (none, charger disconnected or unknown type)
    1 (ac)
    2 (usb)
    3 (wireless)

Change-Id: I8ff4751e521585f94cd421a0edeba04651094bce
Signed-off-by: Youngjae Cho <y0.cho@samsung.com>