ENYO-3934: Set locale from picker upon initialization.

Issue
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The `DatePicker` does not always display the correct date format initially.

Fix
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The root cause is that Safari reports its language as `en-us` while other browsers like Chrome report it as `en-US`. So instead we directly initialize the locale of all of the `DatePicker` controls upon initialization, based on the selection in the locale picker, and not have our sample be reliant on the browser's self-reported language as this technique is more of a fallback.

Notes
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Also opened an ilib PR to normalize the language reported by the browser: https://github.com/enyojs/enyo-ilib/pull/59

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>