Updated xamarin for ios 7 and Windows Phone 8

#### Window Phone 8 Implementation Changes
+ Updated icons 
+ Headings were persisted at the top of the page for the search results / favourites page

#### Android Implementation Changes
+ Minor update to change the property loading image
 + Originally it was the app icon which I felt lead to confusion

#### iOS 7 Implementation Changes
+ Minor update to handle the iOS 7 navigation bar changes
 + Issue is discussed in iOS 7 Transition Guide 

#### Additional Notes
I changed large number of files changed in order to the replace 'PropertyFinder' with 'PropertyCross'.  Whilst the large number of file changes is not ideal, the diffs of the files are clear to ready and no formatting changes have been committed when I did this.