Fault if env vars are not found

[fcassirer]

https://github.com/Jean28518/linux-assistant/blame/b32db3948d51ff34ccc5258e3a53d159a61e85c0/additional/python/get_applications.py#L79

I get:

                                                                                                                                                                  
flutter: Traceback (most recent call last):                                                                                                                        
  File "/usr/lib/linux-assistant/additional/python//get_applications.py", line 79, in <module>                                                                     
    dataDirs = os.getenv("XDG_DATA_DIRS").split(":")                                                                                                               
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                    
AttributeError: 'NoneType' object has no attribute 'split'               

There are a number of places where os.getenv() is used without defaults and result in exceptions when the code runs.

Two such places are get_applications.py#79 and #81. There is a helper in jessentials.py, "get_environment_variable()" but it isn't used.
In addition, on line #81, just assuming "HOME" is an env variable isn't all that useful, instead, perhaps it would be better to defer to HOME if it exists but default to something like:

        from pathlib import Path

       str=str(Path('~').expanduser())
81: if jfolders.does_folder_exist(os.getenv("HOME",str) + "/.local/share/applications"):