feat: upgrade to Angular 9 and Nebular 5 (#5628)

BREAKING CHANGE:
Angular updated to version 9.
Nebular updated to version 5.
`@agm/core` replaced with `@angular/google-maps`.
`ng2-completer` replaced with `@akveo/ng2-completer`, read details [here](https://github.com/akveo/ng2-smart-table/pull/1140#issue-392285957).

angular.json

@@ -11,6 +11,7 @@
         "build": {
           "builder": "@angular-devkit/build-angular:browser",
           "options": {
+            "aot": true,
             "preserveSymlinks": true,
             "rebaseRootRelativeCssUrls": true,
             "outputPath": "dist",
@@ -36,7 +37,6 @@
               "node_modules/@fortawesome/fontawesome-free/css/all.css",
               "node_modules/socicon/css/socicon.css",
               "node_modules/nebular-icons/scss/nebular-icons.scss",
-              "node_modules/angular-tree-component/dist/angular-tree-component.css",
               "node_modules/pace-js/templates/pace-theme-flash.tmpl.css",
               "node_modules/leaflet/dist/leaflet.css",
               "src/app/@theme/styles/styles.scss"
@@ -55,6 +55,12 @@
           },
           "configurations": {
             "production": {
+              "budgets": [
+                {
+                  "type": "anyComponentStyle",
+                  "maximumWarning": "6kb"
+                }
+              ],
               "optimization": true,
               "outputHashing": "all",
               "sourceMap": false,
@@ -172,7 +178,7 @@
   "schematics": {
     "@schematics/angular:component": {
       "prefix": "ngx",
-      "styleext": "scss"
+      "style": "scss"
     },
     "@schematics/angular:directive": {
       "prefix": "ngx"