[sim-plugin] Fixed modem list query

Modem list is no longer available immediately after QOfonoManager has been
constructed (as a result of elimination of blocking D-Bus calls). One has to
wait for modemsChanged or defaultModemChanged signal.

Also, removed QOfonoModem and other unnecessary members from CDSimController,
normalized signal and slot names.
Merge pull request #80 from monich/qofono-fix

Fix modem list query