Refactored DecorationView

- Removed various blank lines

- Refactor parts of def trackAndDrawAttachmentFromView into own method
called create_attachment_decoration_layers

- Added init and initialized  @attachment_decoration_layers using
create_attachment_decoration_layers and initialized arrow_view via
create_arrow_view

- Set a conditional if attachment_point_view && attached_view to run
contained block only when def trackAndDrawAttachmentFromView is called
by a VC subclass of DecorationView

- Compressed some comments from original Obj-C code.

- Removed self. from read calls to attr_accessors.

- Removed checks  of ivars for existence which were no longer required
since some instances are now created in the init - i.e.
create_arrow_view and create_attachment_decoration_layers.
Fix failing spec.