code refactoring

[pr4deepr]

• Define a class for writer so its easier to incorporate multiple formats, initialize and save images. Add flexibility to save images of any dimension (currently only 3d images can be changed..
• Security issue: Currently workflows option runs .py files in a folder specified by user. This is a potential security issue. Add option so user can confirm which files to run.
• Define a function to handle the return types from workflows. For example, if multiple object are returned, they need to be in a tuple. Otherwise, treat it as a single object.
• use plugin_register to add different software support so workflows can be initialised from napari: Using "register_function" to add custom workflows #17