Implements repeat every X days since last completion (Fixes #6941) (#8962)

* Implemented repeat after completion

* Added tests for repeat after completion in shouldDo.test.js

* Remove lastTicked

* Undoes removal of website/client/README.md

website/server/models/task.js

@@ -224,6 +224,8 @@ export let habit = Task.discriminator('habit', HabitSchema);
 export let DailySchema = new Schema(_.defaults({
   frequency: {type: String, default: 'weekly', enum: ['daily', 'weekly', 'monthly', 'yearly']},
   everyX: {type: Number, default: 1}, // e.g. once every X weeks
+  repeatAfterCompletion: {type: Boolean, default: false},
+  lastCompleted: Date,
   startDate: {
     type: Date,
     default () {