Adding MultiSimSettingController class.

MultiSimSettingController will be a central component that makes
sure below rules for multi SIM and subscription grouping.

1) Grouped subscriptions will have same settings for MOBILE_DATA
   and DATA_ROAMING.
2) Default settings updated automatically. It may be cleared or
   inherited within group. If default subscription A switches to
   profile B which is in the same group, B will become the new default.
3) For primary subscriptions, only default data subscription will
   have MOBILE_DATA on.

Bug: 126805933
Test: unittest and manual:
toggle mobile_data, roaming;
switch default setting;
take out SIM cards to make sure above rulesare met.

Change-Id: I53f7fad899cc43c5b460d1bf33b1bc2914f50bc9
Merged-In: I53f7fad899cc43c5b460d1bf33b1bc2914f50bc9