Update view after adding/editing task

[BaderSZ]

Relevant to #8

After adding a task, its title remains empty and is only visible after refreshing the page.

Uncaught (in promise) TypeError: this._innerValue.zone is undefined
    get timezoneId index.esm.js:1536
    toICALJs index.esm.js:3279
    toICALJs index.esm.js:5404
    toICALJs index.esm.js:5408
    toICS index.esm.js:9952
    _callee$ tasks.js:846
    tryCatch tasks.js:26
    _invoke tasks.js:26
    defineIteratorMethods tasks.js:26
    asyncGeneratorStep tasks.js:28
    _next tasks.js:30
    _asyncToGenerator tasks.js:30
    _asyncToGenerator tasks.js:30
    createTask tasks.js:912
    wrappedActionHandler vuex.esm.js:851
    dispatch vuex.esm.js:516
    boundDispatch vuex.esm.js:406
    mappedAction vuex.esm.js:1064
    addTask HeaderBar.vue:92
    submit HeaderBar.vue:13
    VueJS 26
    addCalendar calendars.js:450
    wrappedMutationHandler vuex.esm.js:844
    commitIterator vuex.esm.js:466
    commit vuex.esm.js:465
    _withCommit vuex.esm.js:624
    commit vuex.esm.js:464
    boundCommit vuex.esm.js:409
    ./src/store/calendars.js/getCalendarsAndTrashBin/_callee/_callee$/< calendars.js:727
    _callee$ calendars.js:726
    tryCatch calendars.js:38
    _invoke calendars.js:38
    defineIteratorMethods calendars.js:38
    asyncGeneratorStep calendars.js:40
    _next calendars.js:42
    promise callback*asyncGeneratorStep calendars.js:40
    _next calendars.js:42
    _asyncToGenerator calendars.js:42
    _asyncToGenerator calendars.js:42
    getCalendarsAndTrashBin calendars.js:747
    wrappedActionHandler vuex.esm.js:851
    dispatch vuex.esm.js:516
    boundDispatch vuex.esm.js:406
index.esm.js:1536

[BaderSZ]

The error code is irreleant to the issue, which should be fixed in b3c696d.