Simplify and persist PowerShell session configuration changes

This change improves our session menu so that when the user selects a
different PowerShell version the choice is persisted in their user
settings.  The previous code for managing session configurations has
been mostly removed because it was unnecessarily complex.

We've also added a new "powershell.powerShellExePath" setting to replace
the now deprecated "powershell.developer.powerShellExePath" setting
since this is now a user-level setting.  If a user has the deprecated
setting in their configuration file, we will notify them and fix it
automatically if they wish.

package.json

@@ -351,6 +351,12 @@
       "type": "object",
       "title": "PowerShell Configuration",
       "properties": {
+        "powershell.powerShellExePath": {
+          "type": "string",
+          "default": "",
+          "isExecutable": true,
+          "description": "Specifies the full path to a PowerShell executable. Changes the installation of PowerShell used for language and debugging services."
+        },
         "powershell.startAutomatically": {
           "type": "boolean",
           "default": true,
@@ -384,7 +390,8 @@
         "powershell.developer.powerShellExePath": {
           "type": "string",
           "default": "",
-          "description": "Specifies the full path to a PowerShell executable. Changes the installation of PowerShell used for language and debugging services."
+          "isExecutable": true,
+          "description": "Deprecated. Please use the 'powershell.powerShellExePath' setting instead"
         },
         "powershell.developer.powerShellExeIsWindowsDevBuild": {
           "type": "boolean",

src/main.ts

@@ -126,7 +126,7 @@ export function activate(context: vscode.ExtensionContext): void {
 
     sessionManager.setExtensionFeatures(extensionFeatures);
 
-    var extensionSettings = Settings.load(utils.PowerShellLanguageId);
+    var extensionSettings = Settings.load();
     if (extensionSettings.startAutomatically) {
         sessionManager.start();
     }