Fixes for Model download, Screenshots cancelling and Language sort

[HariSK20]

Related Issue :

• Fixes The Math / equation detection module does not finish downloading #27

Proposed Changes:

• Using the link to tesseract-ocr/tessdata as a backup source, if the required model is not found under tessdata-best

Result:

• The math module can now be installed, And any modules which were removed from tessdata-best.

Additional changes:

• Cancelling screenshot using ESC key would result in the app stopping abruptly

  

  Changes:

  • Fixed minor errors in window.py

  Result:

  • The screenshot can be cancelled without breaking the app

• Opening Languages dialog window would create a lot of errors in when run through the terminal. It prevents sorting of languages by name in the UI.

  

  Changes:

  • Fixed minor issue in language_dialog.py

  Result:

  • Opening Language window will not produce errors.
  • The list of languages are now sorted in order