CSHARP-975: Move caching of connection pools out of MongoServer.
CSHARP-975: Added tests.
CSHARP-977: Remove obsolete DatabaseName from MongoDatabaseSettings and CollectionName and DefaultDocumentType from MongoCollectionSettings.
CSHARP-979: Removed obsolete MongoConnectionStringBuilder class.
CSHARP-979: Let MongoUrl decide if connection string is valid or not.
CSHARP-1037: Port bulk write operations from 1.x to 2.x.
moved all files MongoDB.Driver.Core into a Core folder and changed the default namespace to MongoDB.Driver.
moved most files in MongoDB.Driver.Core.Tests into Core folder and reset the default namespace of the project to MongoDB.Driver.
fixed the namespaces of all the test classes in MongoDB.Driver.Core.Tests.
moved classes in MongoDB.Driver.Core.FunctionalTests into Core folder.
fixed namespaces in MongoDB.Driver.Core.FunctionalTests to be MongoDB.Driver.Core in line with their folder structure.
fixed find-replace mistake with assembly info files.
CSHARP-875: Removed all code from high level driver that now belongs in Core and temporarily replaced it with NotImplementedExceptions.