upgrade to Ionic 4.0 (stable)

What needs to be changed?

Stable version 4.0 of @ionic/angular should be used, and dependencies should be updated.

Also some packages have high priority warnings (npm audit):

# Run  npm install cordova-plugin-ionic-webview@3.1.1  to resolve 1 vulnerability
SEMVER WARNING: Recommended action is a potentially breaking change
┌───────────────┬──────────────────────────────────────────────────────────────┐
│ High          │ Path Traversal                                               │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ cordova-plugin-ionic-webview                                 │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ cordova-plugin-ionic-webview                                 │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ cordova-plugin-ionic-webview                                 │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://nodesecurity.io/advisories/746                       │
└───────────────┴──────────────────────────────────────────────────────────────┘


# Run  npm install --save-dev @angular-devkit/build-angular@0.12.3  to resolve 1 vulnerability
┌───────────────┬──────────────────────────────────────────────────────────────┐
│ High          │ Missing Origin Validation                                    │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Package       │ webpack-dev-server                                           │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Dependency of │ @angular-devkit/build-angular [dev]                          │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ Path          │ @angular-devkit/build-angular > webpack-dev-server           │
├───────────────┼──────────────────────────────────────────────────────────────┤
│ More info     │ https://nodesecurity.io/advisories/725                       │
└───────────────┴──────────────────────────────────────────────────────────────┘


found 2 high severity vulnerabilities in 50943 scanned packages

How is the current state not sufficient?

Beta (unstable) version, old typescript (v2) instead of v3.

Which changes are necessary?

Update of used packages in package.json, eventual refactoring.

Do the proposed changes impact current use cases?

No, except eventual simple refactoring.

cc: @sebastianlange