Add TARGET_USERNAME variable to define username on target distro. Layer can be now used by others also.

usb-moded: Renew config files with fixes for adb (no more rndis while using adbd, it didn't work anyway), sdk(udhcpd.service has been renamed to udhcp-daemon.service to workaround a DBus method call timeout to StartUnit and StopUnit, thanks to this udhcpd's status stays synced between systemd and usb-moded) and mtp modes(enabling the ffs usb mode was required for buteo-mtp to be able to write in /dev/mtp/ep0 and start buteo-session.service which starts buteo-mtp.service as ceres).

usb-moded: Touch /var/lib/misc/udhcpd.leases to remove a warning from udhcpd http://thread.gmane.org/gmane.linux.busybox/17805

usb-moded: Initialize iSerial, iManufacturer and iProduct from Android's properties before starting usb-moded

usb-moded: Provides proper configuration to start udhcpd on modes that activate DHCP and fix a handful of related bugs

usb-moded: Installs a com.meego.usb_moded.service so that usb-moded can be started dynamically by DBus (fixes a boot error message)