Add new prop and prevent default initialize

[Marcoo09]

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In this pull request was:

• Added a value prop to define a default value in case it's necessary
• Fixed a problem from my point of view in which the updater was called each time the Slider is re-rendered.

[Marcoo09]

Related issue #114

[Marvedog]

What's the hold up? This seems like a pretty done deal

[Marcoo09]

What do you mean? My first point it's an improvement to have the ability of define a default value in the slider, for example you use the slider in edit mode and create mode, so the first time you want to render on 0 and the second time in the last value set. My second point it's a bug related the updater is called on the first render without touch anything.