Migrate components to styled-components

Description:

• refactor all components to styled-components with https://github.com/styled-components/styled-components
• each component should have theme prop where you can pass your custom component theme: https://www.styled-components.com/docs/advanced#the-theme-prop

Reason:

When building an application you might need to use only few components and instead of including globally a stylesheet with styles for the whole components library doesn’t make sense.

• As an App developer you want to have components that are self-contained and bring styling with them.
• As an App developer you want to have control over a component and override it’s styling in highly flexible fashion

Hint To quickly check how styled-components work take a look on one of ours component https://github.com/asyncapi/asyncapi-react and quickly play with it https://codesandbox.io/s/5vz8l9zlmn to see how theming works and that in case of styled-component for global stylesheet you need only a font reference

[bcullman]

It looks like for this item, style would be served directly from this repo. I think we need to decide NOW what our relationship is with https://github.com/SAP/fundamental.

1. reference https://github.com/SAP/fundamental is what we should aspire to, but each fundamental-[X] repos (react/vue/ngx) is free to write their own CSS

2. dependency use CSS from https://github.com/SAP/fundamental directly, all fundamental-[X] repos (react/vue/ngx) are required to emit the same HTML, but left to their implement in the manner best suited to that framework.

Personally, I vote for dependency.

Additionally, during transition, SAP Concur will require the ability to use these components “style-less” (we will provide our own style)

[magicmatatjahu]

@derberg The styles downloaded from the package is a good option. At the moment I do not have any better solution.

A few comments regarding writing styled components:

• write always styled components in separate file, like a styled.js,
• name styled components with prefix of appropriate component like ButtonContent ButtonWrapper etc.