Bug 921971 - [DSDS][FDN] Manage FDN list for both SIMs

Implemented:

AC1: I expect to have the same FDN functionality as in the single SIM implementation for each of the SIMs.
AC2: I expect to have the FDN list active only for the current default SIM for Voice
AC3: I expect SIM2 to still remember the data (though disabled) when SIM1 is the default for Voice, and vice versa.

This fix makes it possible to have independent Fixed Dialing Numbers for each SIM card in the phone. A new function `getIccByIndex` has been introduced in `utils.js` that selects the currently selected ICC object without the user having to specify the particular index, although it allows that too (used in `sim_dialog.js`, for example.

Instances of `IccHelper` have been replaced by the result of calls to `getIccByIndex`.