Update of the Serbian translation

Change-Id: If244aabe80414cc0202f3d18c0d0defc6b0c47bf
Reviewed-on: http://gerrit.rockbox.org/1016
Reviewed-by: Michael Giacomelli <giac2000@hotmail.com>
Enable battery charging detection for iBasso DX50/DX90.

This changes iBasso DX50/DX90 config from CHARGING_SIMPLE (Simple, hardware
controlled charging (CPU cannot read charger state but may read when power is
plugged-in) to CHARGING_MONITOR (Hardware controlled charging with monitoring
(CPU is able to read HW charging state and when power is plugged-in)).

Not really usefull at the moment, since USB connection (charging) is not (yet)
gracefully handled for iBasso devices.

Change-Id: I55da81b10637d4de88d713ea5eba08eb59bc629f
Reviewed-on: http://gerrit.rockbox.org/1010
Reviewed-by: Michael Giacomelli <giac2000@hotmail.com>