Add error flashes to Design view

What does this MR do?

Adds warning and error flashes created by our createFlash method to the enlarged design view in design management (originally raised in #36925 (closed)).

UPDATE: Adds GlAlert to the Design view so that we can capture errors and display feedback to user (originally raised in #36925 (closed))

How to test?

1. Open Design view
2. gdk stop
3. Try to start a new discussion
4. Observe error

Screenshots

Desktop

![Screen_Shot_2019-12-06_at_1.09.19_pm](/uploads/67492216e873e4436877dcf1b264c1bc/Screen_Shot_2019-12-06_at_1.09.19_pm.png)

Mobile

![Screen_Shot_2019-12-06_at_1.09.33_pm](/uploads/ee34e2bd0742a0364e3048bec09cc2d1/Screen_Shot_2019-12-06_at_1.09.33_pm.png)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers