* Release mo dev guide refactoring (#3266)
* Updated MO extension guide
* Minor change and adding svg images
* Added additional information about operation extractors. Fixed links and markdown issues
* Added missing file with information about Caffe Python layers and image for MO transformations dependencies graph
* Added section with common graph transformations attributes and diagram with anchor transformations. Added list of available front phase transformations
* Added description of front-phase transformations except the scope-defined and points defined. Removed legacy document and examples for such transformations.
* Added sections about node name pattern defined front phase transformations. Copy-pasted the old one for the points defined front transformation
* Added description of the rest of front transformations and and all middle and back phase transformations
* Refactored Legacy_Mode_for_Caffe_Custom_Layers and updated the Customize_Model_Optimizer with information about extractors order
* Added TOC for the MO Dev guide document and updated SVG images with PNG ones
* Fixed broken link. Removed redundant image
* Fixed broken links
* Added information about attributes 'run_not_recursively', 'force_clean_up' and 'force_shape_inference' of the transformation
* Code review comments
* Added a section about `Port`s
* Extended Ports description with examples
* Added information about Connections
* Updated MO README.md and removed a lot of redundant and misleading information
* Updates to the Customize_Model_Optimizer.md
* More updates to the Customize_Model_Optimizer.md
* Final updates for the Customize_Model_Optimizer.md
* Fixed some broken links
* More fixed links
* Refactored Custom Layers Guide: removed legacy and incorrect text, added up-to-date.
* Draft implementation of the Custom layer guide example for the MO part
* Fixed broken links using #. Change layer->operation in extensibility documents
* Updated Custom operation guide with IE part
* Fixed broken links and minor updates to the Custom Operations Guide
* Updating links
* Layer->Operation
* Moved FFTOp implementation to the template extension
* Update the CMake for template_extension to build the FFT op conditionally
* Fixed template extension compilation
* Fixed CMake for template extension
* Fixed broken snippet
* Added mri_demo script and updated documentation
* One more compilation error fix
* Added missing header for a demo file
* Added reference to OpenCV
* Fixed unit test for the template extension
* Fixed typos in the template extension
* Fixed compilation of template extension for case when ONNX importer is disabled
Co-authored-by: Alexander Zhogov <alexander.zhogov@intel.com>