[MO] Align MO namespaces (#7708)

* Moved and merged mo/ and extensions/ into openvino/tools/mo

* edited imports

* edited docs to use mo script from entry_point

* edited MO transformations list loading and setup.py

* changed full path -> 'mo' entry point in docs (leftovers)

* corrected package_BOM

* updated resolving --transformation_config in cli_parser.py

* pkgutil-style __init__.py, added summarize_graph into entry points

* updated DOCs for the new --transformations_config

* fix select

* updated install instructions, fixed setup.py for windows and python_version < 3.8

* fixed typo in requirements.txt

* resolved conflicts

* removed creating custom __init__.py from setup.py

* corrected folder with caffe proto

* corrected loading user defined extensions

* fix openvino.tools.mo import in serialize.py

* corrected layer tests for new namespace

* fix in get_testdata.py

* moved model-optimizer into tools/

* renamed import in POT

* corrected mo.yml

* correct CMakeLists.txt for the newest tools/mo

* corrected find_ie_version.py

* docs and openvino-dev setup.py update for the newest tools/mo

* miscellaneous leftovers and fixes

* corrected CI files, pybind11_add_module in CMakeLists.txt and use of tools/mo path instead of tools/model_optimizer

* add_subdirectory pybind11 for tools/mo

* POT path fix

* updated setupvars.sh setupvars.bat

* Revert "updated setupvars.sh setupvars.bat"

This reverts commit c011142340.

* removed model-optimizer env variables from setupvars

* updated CMakeLists.txt to pack MO properly with tests component

* corrected left imports, corrected loading requirements for layer tests

* mo doc typo correction

* minor corrections in docs; removed summarize_graph from entry_points

* get_started_windows.md, MonoDepth_how_to.md corrections, mo path corrections

docs/HOWTO/Custom_Layers_Guide.md

@@ -137,7 +137,7 @@ and [Convert Your TensorFlow* Model](../MO_DG/prepare_model/convert_model/Conver
 for more details and command line parameters used for the model conversion.
 
 ```bash
-./<MO_INSTALL_DIR>/mo.py --input_model <PATH_TO_MODEL>/wnet_20.pb -b 1
+mo --input_model <PATH_TO_MODEL>/wnet_20.pb -b 1
 ```
 > **NOTE:** This conversion guide is applicable for the 2021.3 release of OpenVINO and that starting from 2021.4
 > the OpenVINO supports this model out of the box.
@@ -258,7 +258,7 @@ The implementation should be saved to the file `mo_extensions/front/tf/ComplexAb
 
 Now it is possible to convert the model using the following command line:
 ```bash
-./<MO_INSTALL_DIR>/mo.py --input_model <PATH_TO_MODEL>/wnet_20.pb -b 1 --extensions mo_extensions/
+mo --input_model <PATH_TO_MODEL>/wnet_20.pb -b 1 --extensions mo_extensions/
 ```
 
 The sub-graph corresponding to the originally non-supported one is depicted in the image below:
@@ -322,7 +322,7 @@ The result of this command is a compiled shared library (`.so` or `.dll`). It sh
 application using `Core` class instance method `AddExtension` like this
 `core.AddExtension(std::make_shared<Extension>(compiled_library_file_name), "CPU");`.
 
-To test that the extension is implemented correctly we can run the "mri_reconstruction_demo.py" with the following content:
+To test that the extension is implemented correctly we can run the "mri_reconstruction_demo" with the following content:
 
 @snippet mri_reconstruction_demo.py mri_demo:demo