This adds the timezones to the step validation and renders an error when an invalid timezone is imported.

How to test:
1. import a blueprint with invalid timezone "foo"
2. select a target
3. go to Registration step
4. click on "Review and finish" button

Current behaviour:

• the "Create" button is disabled, but when navigating to Timezone step no error is displayed

After update:

• there is an error rendered under the timezone select