Add ColorField

[lukasan]

What happened to #31? Is there any way to have colour picker functionality inside the manager?

All I can do is just use a StringField and use its input as a hex value in .cshtml. This is really hacky.

[tidyui]

As the core package is content oriented we have tried to stay clear of fields that are not content focused. However we have talked about creating an add-on package with more web-oriented fields, like color pickers, YouTube media and so on.

[honzajscz]

Such a package would be extremely handy!

[govi2010]

Hello @tidyui ,

I have made some progress on this.
I have used vue-color package and made some progress.

I have pushed my code my master branch(forked repo). If you can review and suggest some changes.

[govi2010]

Doing CSS improvement this weekend.