sl-date-range-picker: "startDateValue" should not be able to be set when it is less than "minDate"

[juwara0]

Provide a fix for "startDateValue" being able to be set when it is less than "minDate" and then verify the fix by turning the skipped test below back on.

This test fails:

test( '"startDateValue" cannot be less than "minDate"', function( assert ) {

this.render( hbs`
    {{sl-date-range-picker
        minDate="09/28/2015"
        startDateValue="09/25/2015"
    }}
` );

assert.strictEqual(
    this.$( '>:first-child' ).find( '.sl-daterange-start-date' ).find( 'input' ).val(),
    '09/28/2015',
    'The "startDateValue" is not less than the "minDate"'
);

});

[Yogeswar]

I'm working on this.

[Yogeswar]

This issue also addresses #871, #874, #875

[SpikedKira]

Should be resolved by #1458