Use proper cache and config locations

[hmenke]

Currently we dump all of the state of the pairinteraction GUI into ~/.pairinteraction. This goes against all desktop specifications on all operating systems and should be fixed. Unfortunately this is platform dependent, so we need to distinguish:

• Config Directory:

  Linux: $XDG_CONFIG_HOME/pairinteraction or ~/.config/pairinteraction
  Windows: %APPDATA%\pairinteraction
  MacOS: ~/Library/Preferences/pairinteraction

• Cache directory:

  Linux: $XDG_CACHE_HOME/pairinteraction or ~/.cache/pairinteraction
  Windows: %LOCALAPPDATA%\pairinteraction
  MacOS: ~/Library/Caches/pairinteraction

[hmenke]

Here is a first approximation, but it has to be tested on all platforms.

diff --git a/pairinteraction_gui/pairinteraction/app.py b/pairinteraction_gui/pairinteraction/app.py
index a7459045..e99b239c 100644
--- a/pairinteraction_gui/pairinteraction/app.py
+++ b/pairinteraction_gui/pairinteraction/app.py
@@ -483,21 +483,34 @@ class MainWindow(QtWidgets.QMainWindow):
         self.path_cpp_complex = os.path.join(self.path_base, self.path_workingdir, "pairinteraction-complex")
         self.path_quantumdefects = os.path.join(self.path_base, self.path_workingdir, "databases/quantum_defects.db")
 
-        if os.name == "nt":
-            self.path_out = os.path.join(self.userpath, "pairinteraction/")
+        if sys.platform == "win32":
+            self.path_config = os.path.expandvars(r'%APPDATA%\pairinteraction')
+            if r'%APPDATA%' in self.path_config
+                self.path_config = os.path.expanduser(r'~\AppData\Local\pairinteraction')
+            self.path_cache = os.path.expandvars(r'%LOCALAPPDATA%\pairinteraction')
+            if r'%LOCALAPPDATA%' in self.path_config
+                self.path_cache = os.path.expanduser(r'~\AppData\Local\pairinteraction')
+        elif sys.platform == "darwin":
+            self.path_config = os.path.expanduser(r'~/Library/Preferences/pairinteraction')
+            self.path_cache = os.path.expanduser(r'~/Library/Caches/pairinteraction')
         else:
-            self.path_out = os.path.join(self.userpath, ".pairinteraction/")
-        self.path_cache = os.path.join(self.path_out, "cache/")
+            self.path_config = os.path.expandvars(r'$XDG_CONFIG_HOME/pairinteraction')
+            if r'$XDG_CONFIG_HOME' in self.path_config:
+                self.path_config = os.path.expanduser(r'~/.config/pairinteraction')
+            self.path_cache = os.path.expandvars(r'$XDG_CACHE_HOME/pairinteraction')
+            if r'$XDG_CACHE_HOME' in self.path_cache:
+                self.path_cache = os.path.expanduser(r'~/.cache/pairinteraction')
+
         self.path_cache_wignerd = os.path.join(self.path_cache, "wignerd/")
-        self.path_lastsettings = os.path.join(self.path_out, "lastsettings/")
+        self.path_lastsettings = os.path.join(self.path_config, "lastsettings/")
 
         self.path_system_last = os.path.join(self.path_lastsettings, "lastsettings.sconf")
         self.path_plot_last = os.path.join(self.path_lastsettings, "lastsettings.pconf")
         self.path_view_last = os.path.join(self.path_lastsettings, "lastview.json")
         self.path_cache_last = os.path.join(self.path_lastsettings, "lastcache.json")
 
-        self.path_config = os.path.join(self.path_out, "conf.json")
-        self.path_version = os.path.join(self.path_out, "version.json")
+        self.path_config = os.path.join(self.path_config, "conf.json")
+        self.path_version = os.path.join(self.path_config, "version.json")
 
         self.proc = None
 
@@ -834,15 +847,8 @@ class MainWindow(QtWidgets.QMainWindow):
                 sys.exit()
 
         # Create directories
-        if not os.path.exists(self.path_out):
-            os.makedirs(self.path_out)
-            if os.name == "nt":
-                import ctypes
-
-                FILE_ATTRIBUTE_HIDDEN = 0x02
-                ret = ctypes.windll.kernel32.SetFileAttributesW(self.path_out, FILE_ATTRIBUTE_HIDDEN)
-                if not ret:
-                    raise ctypes.WinError()
+        os.makedirs(self.path_config, exist_ok=True)
+        os.makedirs(self.path_cache, exist_ok=True)
 
         if not os.path.isfile(self.path_version):
             with open(self.path_version, "w") as f: