Resize Dropdown and Colopicker to their full width

[SylvainCorlay]

Colopicker and Dropdown now use all the available width.

• The dropdown button and color-picker buttons now have the same width (28px).
• A new boolean attribute short is added to the color picker specifying whether the text box should be displayed or not.
• If the text box is displayed, the widget width is @widget-width. If not, it is @widget-width-short.
• In the short mode, if there is a description, the color picker button is justified to the right, and if there is only the color picker button to displayed, it is on the left.

[SylvainCorlay]

@jdfreder green button? I have got another one coming on the top of it fixing slider layouts.

[jdfreder]

Sounds good! Thanks Sylvain!