Added image attaching for iOS Guide's Twitter

Added image attaching for iOS Guide's Twitter
Merge pull request #2718 from picobots/develop

Added image attaching for iOS Guide's Twitter
Avoiding loading content twice when a path is passed to us using different path separators or casing.
Fixed logic error.
Merge pull request #2722 from SickheadGames/CopyToOutput

Fixed logic error when copying a file to its output folder
Merge pull request #2721 from SickheadGames/FixPathSepAndCase

Fixed "Loading Content Twice" bug.
Fixed incorrect parsing of Number type.
Fixed cases of int.Parse() and float.Parse() to use the invariant culture.
Added a comment to clarify things.
Merge pull request #2724 from SickheadGames/mgfxculture

MGFX Fixes
Fixed possible ArgumentNullException in ContentTypeReaderManager.

ContentTypeReader.TargetType can be null, e.g. for ExternalReferenceReader.
Merge pull request #2725 from DigitalRune/contentreader

Fixed possible ArgumentNullException in ContentTypeReaderManager.