Split Change and ChangeSummary out

--HG--
rename : src/TeamCitySharp/DomainEntities/Change.cs => src/TeamCitySharp/DomainEntities/ChangeSummary.cs
Fixing Changes and Files for TeamCity 7

--HG--
rename : src/TeamCitySharp/DomainEntities/File.cs => src/TeamCitySharp/DomainEntities/FileData.cs