List valid modem technologies in RadioSettings interface

This branch adds ModemTechnologies property to org.ofono.RadioSettings interface. This property lists valid RATs for the modem. The changes also ensure that org.ofono.RadioSettings is available when there is no SIM, which is required to access FastDormancy (needed for power management) and ModemTechnologies (needed by system settings) properties.
Not sure why you did this?  Again, you can just drop 'strs' altogether, and just use 'rats_strs' directly in the dict_append_array() call like: this:

ofono_dbus_dict_append_array(&dict, "ModemTechnologies", DBUS_TYPE_STRING, rats_strs);

This builds with no warnings for me, and the code works as it's supposed to...