Added a config for disabling the window reload

[kittaakos]

What it does

Set the disallowReloadKeybinding application config to true if you
want to disable the browser window reload with Ctrl/Cmd+R.

The config does not affect the behavior of the app if it is running
in a browser environment.

How to test

Modify your package.json for the electron example, and try to reload with Ctrl/Cmd+R:

git diff ./examples/electron/package.json 
diff --git a/examples/electron/package.json b/examples/electron/package.json
index ffb2ba700..b5271db01 100644
--- a/examples/electron/package.json
+++ b/examples/electron/package.json
@@ -7,7 +7,8 @@
     "target": "electron",
     "frontend": {
       "config": {
-        "applicationName": "Theia Electron Example"
+        "applicationName": "Theia Electron Example",
+        "disallowReloadKeybinding": true
       }
     }
   },

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[spoenemann]

It worked for me as described after running yarn --cwd examples/electron build.