Changes for Tensorflow 2.5.0

Fix problem for XML files which additional tags

Update training.rst

Previous link to the Tensorflow 1 Detection Model Zoo, https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/detection_model_zoo.md, leads to a page that didn't exist anymore (Error 404). 
The new link to the Tensorflow 1 Detection Model Zoo should be: https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/tf1_detection_zoo.md.

Update README.md

Removed `,`s in `conda install` which throw an error

Fix missing images

Updated to TensorFlow 1.14

added cython

while executing "make" command in "COCO API installation" in linux ubuntu got  "gcc: error: pycocotools/_mask.c: No such file or directory
"
this thread : cocodataset/cocoapi#141
solved the issue ie: after installing cython

added cython

while executing "make" command in "COCO API installation" in linux ubuntu got  "gcc: error: pycocotools/_mask.c: No such file or directory
"
this thread : cocodataset/cocoapi#141
solved the issue ie: after installing cython

Minor fixes and updates