Improved Makefile and python scripts for Validation CER plotting

[Shreeshrii]

Improvements over current version:

• Uses a Makefile for validation and plotting (still needs to be run twice to get latest checkpoints validation)
• Allows for missing validation logs till the Checkpoint CER falls below 10%
• Plots saved in data/MODEL_NAME/plot directory
• Training log is used from data/MODEL_NAME.log
• Plots have been enhanced to display number of lines in list.train, list.eval and list.validate.
• Line plot is used only for CER every 100 iterations.
• Scatter points are used for the values for Checkpoint CER, Eval CER and Validation CER
• Labels added to display minimum CER value with the learning iteration number
• Allows use of custom validation lists from data/MODEL_NAME directory
• Use tsv instead of csv file extension for better display on Github

See sample plots below:

Training from Scratch - Sanskrit in Devanagari + IAST + English

Training with START_MODEL=san, PlusMinus - Sanskrit in Devanagari

[Shreeshrii]

PR #214, #215 and #217 are needed to be applied for this to work.

[Shreeshrii]

see https://github.com/Shreeshrii/tesstrain/tree/ben/data/ben for training results and reports for Bengali using groundtruth provided in https://groups.google.com/g/tesseract-ocr/c/kpF4jmik6W0/m/bo4HL0ejBgAJ

I have changed the plots to also display the best fit curve for the CER values. New plots look like the following:

I will try and convert the bash scripts creating ocreval reports to make.