[mms-settings] Changed dconf path for MMS settings

Previously, MMS settings were stored right in the IMSI directory at the
root of the dconf namespace. They have been moved to /imsi/ folder and
MMS settings now live in the mms subfolder, i.e. /IMSI/ -> /imsi/IMSI/mms/

Old settings are migrated to the new location the first time they are
requested. Instead of GSettings we now directly use DConf because it
appears to be impossible to properly implement migration with GSettings.
That makes gschema obsolete but we need to keep it around for backward
compatibility reasons.
Merge pull request #49 from monich/dconf

Changed dconf path for MMS settings
[mms-engine] Added getVersion D-Bus API

Allows applications to determine which version of mms-engine is installed.
Merge pull request #50 from monich/version

Added getVersion D-Bus API
[mms-engine] Added migrateSettings D-Bus API
[mms-settings] Be tolerant to variations of integer data types

We will accept any kind of integer where we expect uint32 provided
that its value falls into [0..UINT_MAX] range.
Merge pull request #52 from monich/dconf_uint32

Be tolerant to variations of integer data types
Merge pull request #51 from monich/migrate

Added migrateSettings D-Bus API
[mms-settings-dconf] Fixed memory leak