Added additional constructor overloads for DICOM exception types

* Exceptions now all implement 3 public constructors and the serialization
  constructor.
* Exceptions now support format args in overloads with a message parameter.

Fixes #13
Added designer properties to control icon scaling size in BindingTreeView

* Size properties now exist for changing the target scaling size of icons in
  the context menu and the toolbar.

Fixes #14
Added DicomStreamWriter option to encode for digital signature MAC generation

* The DigitalSignatureMacEncoding option overrides certain behaviour in the
  DicomStreamWriter, skipping length fields for SQ and undefined length OB
  (i.e. encapsulated pixel data) attributes, skipping length fields for items,
  skipping item delimitation tags, and always including a terminating sequence
  delimitation item without a corresponding length field.
* Also fixed a bug in the DicomFragmentSequence class where cloning the
  attribute does not also clone the offset table, if one exists.

Fixes #15