Notify user when config directory can't be created because there is already a file with the same name

[micahellison]

Fixes #659. It catches an exception in the XDG method and lets the user know exactly where the problem is.

While working on this, I noticed that a ton of configuration code was in the install.py file, so I moved it to config.py as necessary and updated the tests to use patches instead of a global. The configuration code still needs a lot of work but I hope this is at least a step in the right direction.

I couldn't come up with a good strategy to automatically test this issue, since XDG is essentially global to the program. Here's my manual test:

C:\dev\jrnl>copy con C:\Users\micah\.config\jrnl
this is a text file
^Z
        1 file(s) copied.

C:\dev\jrnl>jrnl --ls
The path to your jrnl configuration directory is a file, not a directory:
C:\Users\micah\.config\jrnl
Removing this file will allow jrnl to save its configuration.

C:\dev\jrnl>del C:\Users\micah\.config\jrnl

C:\dev\jrnl>jrnl --ls
Path to your journal file (leave blank for C:\Users\micah\.local\share\jrnl\journal.txt):
Do you want to encrypt your journal? You can always change this later [y/N]
Journals defined in C:\Users\micah\.config\jrnl\jrnl.yaml
 * default -> C:\Users\micah\.local\share\jrnl\journal.txt

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have tested this code locally.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.
• All tests pass.

[wren]

🤠