implement search service

package.json

@@ -192,7 +192,7 @@
     "@angular/compiler-cli": "5.2.0",
     "@ngtools/webpack": "1.10.2",
     "@types/lowdb": "^1.0.1",
-    "@types/lunr": "2.1.5",
+    "@types/lunr": "^2.1.6",
     "@types/node": "8.0.19",
     "@types/node-forge": "0.7.1",
     "@types/papaparse": "4.1.31",
@@ -246,7 +246,7 @@
     "electron-updater": "3.0.3",
     "keytar": "4.2.1",
     "lowdb": "1.0.0",
-    "lunr": "2.1.6",
+    "lunr": "2.3.1",
     "node-forge": "0.7.1",
     "nord": "0.2.1",
     "papaparse": "4.3.5",