[Feature Request] Format should support literal strings

[alex-dunn]

Existing Component

Yes

Component Name

DatePicker

Description

The format in datepicker does not support literal strings.
This means that if I want to have a date formatted as WC 22/04/2019 I would use the format WC dd/MM/yyyy. In the current version of the component this would result in the string 17C 22/04/2019.
The latest version of fecha allows the "[...]" syntax to specify strings that should be treated literally. I could use the format [WC] dd/MM/yyyy to get the desired results.

Example:
https://codepen.io/anon/pen/LvJzOr