Fix compile errors in PCL project

Related to ReadOnlyCollection and CultureInfo instantiation.

Author: angularsen

Src/Scripts/Include-GenerateUnitSystemDefaultSourceCode.ps1

@@ -35,7 +35,7 @@ namespace UnitsNet
     public partial class UnitSystem
     {
         private static readonly ReadOnlyCollection<UnitLocalization> DefaultLocalizations
-            = new List<UnitLocalization>
+            = new ReadOnlyCollection<UnitLocalization>(new List<UnitLocalization>
             {
 "@;
     foreach ($unitClass in $unitClasses) 
@@ -72,7 +72,7 @@ namespace UnitsNet
 "@;
     }
 @"
-            }.AsReadOnly();
+             });
     }
 }
 "@;

Src/UnitsNet/CustomCode/UnitSystem.cs

@@ -245,7 +245,7 @@ private void LoadDefaultAbbreviatons([NotNull] CultureInfo culture)
                 foreach (CulturesForEnumValue ev in localization.EnumValues)
                 {
                     int unitEnumValue = ev.Value;
-                    CultureInfo usCulture = CultureInfo.GetCultureInfo("en-US");
+                    var usCulture = new CultureInfo("en-US");
 
                     // Fall back to US English if localization not found
                     AbbreviationsForCulture matchingCulture =

Src/UnitsNet/GeneratedCode/UnitSystem.Default.g.cs

@@ -32,7 +32,7 @@ namespace UnitsNet
     public partial class UnitSystem
     {
         private static readonly ReadOnlyCollection<UnitLocalization> DefaultLocalizations
-            = new List<UnitLocalization>
+            = new ReadOnlyCollection<UnitLocalization>(new List<UnitLocalization>
             {
                 new UnitLocalization(typeof (AngleUnit),
                     new[]
@@ -804,6 +804,6 @@ private static readonly ReadOnlyCollection<UnitLocalization> DefaultLocalization
                                 new AbbreviationsForCulture("ru-RU", "Американская унция"),
                             }),
                     }),
-            }.AsReadOnly();
+             });
     }
 }

Src/UnitsNet/I18n/AbbreviationsForCulture.cs

@@ -32,8 +32,8 @@ internal class AbbreviationsForCulture
 
         public AbbreviationsForCulture(string cultureName, params string[] abbreviations)
         {
-            Cult = CultureInfo.GetCultureInfo(cultureName);
-            Abbreviations = abbreviations.ToList().AsReadOnly();
+            Cult = new CultureInfo(cultureName);
+            Abbreviations = new ReadOnlyCollection<string>(abbreviations.ToList());
         }
     }
 }

Src/UnitsNet/I18n/CulturesForEnumValue.cs

@@ -33,7 +33,7 @@ internal class CulturesForEnumValue
         public CulturesForEnumValue(int value, IEnumerable<AbbreviationsForCulture> cultures)
         {
             Value = value;
-            Cultures = cultures.ToList().AsReadOnly();
+            Cultures = new ReadOnlyCollection<AbbreviationsForCulture>(cultures.ToList());
         }
     }
 }

Src/UnitsNet/I18n/UnitLocalization.cs

@@ -34,7 +34,7 @@ internal class UnitLocalization
         public UnitLocalization(Type unitEnumType, IEnumerable<CulturesForEnumValue> enumValues)
         {
             UnitEnumType = unitEnumType;
-            EnumValues = enumValues.ToList().AsReadOnly();
+            EnumValues = new ReadOnlyCollection<CulturesForEnumValue>(enumValues.ToList());
         }
     }
 }