[New feature]: label box can rotate by using short cut 'x' or 'c', but only support rotate one box at the same time

Fix a bug in PPOCRLabel

New functions: Open the dataset folder, image rotation, add shortcut key description, repair the direction shortcut key movement function under batch processing 

# Conflicts:
#	PPOCRLabel/libs/resources.py

改为大写

Solve the problem that the exported image is displayed as a mirror image after counterclockwise labeling

Spelling mistake, detection box missing,etc.

* Update readme

* Optimize the labeling experience