[libcalamares] Consistent namespace usage in partition service

- The sub-directories under libcalamares (e.g. Utils, ..)
   all live in namespace CalamaresUtils (well, except for Logger).
   The services (e.g. subdirs other than utils/) live in their
   own nested namespace, so partitioning should go into
   CalamaresUtils::Partition for consistency.

src/modules/partition/core/PartitionLayout.cpp

@@ -86,10 +86,10 @@ PartitionLayout::addEntry( PartitionLayout::PartitionEntry entry )
 }
 
 PartitionLayout::PartitionEntry::PartitionEntry( const QString& size, const QString& min, const QString& max )
+    : partSize( size )
+    , partMinSize( min )
+    , partMaxSize( max )
 {
-    partSize = Calamares::PartitionSize( size );
-    partMinSize = Calamares::PartitionSize( min );
-    partMaxSize = Calamares::PartitionSize( max );
 }
 
 bool