ColorPalette (ui5-color-palette): New component

[fifoosid]

Is your feature request related to a problem? Please describe.
A color palette component should be implemented. Reference: https://sapui5.hana.ondemand.com/#/entity/sap.m.ColorPalette/sample/sap.m.sample.ColorPalette

Additional context
The current use case: this component will be used in responsive popover

[ilhan007]

Background
Hello @SAP/ui5-webcomponents-topic-b we need a color palette component for the TextEditor (RichTextEditor) we are currently building to allow users select text's color and text's background-color. Also, the component can be used to build ColorPalettePopover if we decide it is necessary and find it useful.

Reference
https://sapui5.hana.ondemand.com/#/entity/sap.m.ColorPalette/sample/sap.m.sample.ColorPalette

Main Use-Case
The palette will be mainly used inside a ui5-popover or ui5-responsive-popover

Restrictions
As in openui5, we would like to display up to 15 coloured squares as part of the palette.

API (This is just a proposal)

1. Definition of the colors the user clack select of, either via property, or via slot

// Variant 1: string property of comma separated CSS colors:
properties: {
  colors: {
     type: String
  }
}

<ui5-color-palette colors="darkblue, #444444, white, black, rgb(0,0,0), hsla(50%,10%,30%,0.5), #fff, green">

// Variant 2: with abstract element as a slot

slots: {
   colors: {
       type: HTMLElement
   }
}

<ui5-color-palette> 
 <ui5-color-palette-entry value="darkblue">
 <ui5-color-palette-entry value="#333">
 <ui5-color-palette-entry value="#444">
</ui5-color-palette> 

2. We need to fire an event when the users interacts/clicks the coloured squares (SPACE, ENTER as well)

Events: {
    click: {
       details: {
          color: {
              type: "String"
           }
       }
    }
}

Keyboard handling
By the existing spec - at least ArrowKeys navigation + ENTER and SPACE

Screen Reader
By the existing spec

Playground Sample