Added "GetAll" Functions to Database handler

These functions return all items of a single kind.
We need to think of if we should handle more logic within sqlite
queries (eg. more specific like get all characters of this game) or if we would
like to handle this on apps side.

app/build.gradle

@@ -7,8 +7,8 @@ android {
         applicationId "com.de.aldo_apps.aldo.mariokartcircuitselector"
         minSdkVersion 16
         targetSdkVersion 25
-        versionCode 5
-        versionName "0.1.5"
+        versionCode 6
+        versionName "0.1.6"
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
     }
     buildTypes {