Add ability to load 2Mb+ files

[avishnyakov]

Currently CSOM allows to upload only < 2Mb files. Not cool, REST should be used.

[avishnyakov]

Test with CSOM and http://mysharepointlearnings.wordpress.com/2014/06/30/provider-hosted-app-upload-large-files-using-csom/
https://gist.github.com/garima2510/b1167e611ffb495848ec#file-uploadfilelarge-cs

var spContext = SharePointContextProvider.Current.GetSharePointContext(HttpContext, SPHostUrl);

using (var clientContext = spContext.CreateUserClientContextForSPAppWeb())
{
    if (clientContext != null)
    {
        //file is uploaded file. Could be read from Request.Files
        using (FileStream fs = new FileStream(file.FileName, FileMode.Open))
        {
            //code for file size > 2MB. tested upto 50MB
            FileCreationInformation newFile = new FileCreationInformation();
            newFile.ContentStream = fs;
            newFile.Url = Path.GetFileName(file.FileName);
            newFile.Overwrite = true;

            List docs = clientContext.Web.Lists.GetByTitle("List_Name");
            Microsoft.SharePoint.Client.File uploadFile = docs.RootFolder.Files.Add(newFile);
            clientContext.Load(uploadFile);
            clientContext.ExecuteQuery();
        }
    }
}

[SubPointSupport]

Covered with SPMeta2.Regression.Tests.Impl.Scenarios.ModuleFileScenariousTest implementation for 1, 5, 15, 25 and 50Mb generated files.