ViewModel refactoring: Permissions part

Add MyDbHelper and MyRepository, use database to store dhizuku clients,
fix #168

app/src/main/java/com/bintianqi/owndroid/MyDbHelper.kt

@@ -0,0 +1,15 @@
+package com.bintianqi.owndroid
+
+import android.content.Context
+import android.database.sqlite.SQLiteDatabase
+import android.database.sqlite.SQLiteOpenHelper
+
+class MyDbHelper(context: Context): SQLiteOpenHelper(context, "data", null, 1) {
+    override fun onCreate(db: SQLiteDatabase) {
+        db.execSQL("CREATE TABLE dhizuku_clients (uid INTEGER PRIMARY KEY," +
+                "signature TEXT, permissions TEXT)")
+    }
+    override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
+
+    }
+}