feat: extend functionality of the tabs component

[maylukas]

I tried to use the Tabs component in a small demo / test app and found some aspects that might need changing:

• The tab sizes with the content which is due to rendering the content within the header item.
  
• The state of the tabs component can't be controlled externally and also there is no callback to observe any changes
• The component will always rerender since the tabs are passed as a list (the reference changes every time). If the tabs would be passed as children, the change detection of react would work
• Rendering non-text content fails
• The interface feels a bit non-react-idiomatic :) Passing the tabs as children with their respective content seems to fit better (maybe just personal taste).

I implemented another tabs component as a suggestion and would be happy if you could give feedback on this.

There are also some things I probably didn't get right:

• I probably didn't follow your style guide because I didn't find a reference to it :) If you let me know, I will fix my issues (maybe provide an editorconfig?).
• I used typescript since I saw the issue regarding a possible change of the implementation language to typescript Typescript Support  #32 so I figured I could provide an example. If you want me to use javascript I can change that (switching to typescript / providing type definitions would be great though :) )
• The playground doesn't work / needs to be implemented as I didn't quite figure out what was required to control the props of children.
• The tabs component does not support overflow content as I wasn't sure how this should be done according to the Fiori 3 guidelines (is there an officially available reference?). It would be possible to overflow the tabs if the number of tabs exceeds a certain amount (e.g. passed as a prop).
• I didn't include the react-router integration as I am not sure if this is the right place for it. The choice of the routing framework (or a lack thereof) should be up to the downstream application. Let me know what you think about this.

[CLAassistant]

All committers have signed the CLA.

[CodesOfRa]

Also check @chrismanciero 's branch for typescript https://github.com/SAP/fundamental-react/tree/typescript-conversion

[maylukas]

Ah cool stuff! I wasn't aware that this is already in progress. I am going to rebase onto the typescript-conversion branch.

[maylukas]

Should I create the pull request against the typescript-conversion branch? Or is it planned to merge the typescript branch into master any time soon?

[CodesOfRa]

I think it's best to create a PR against typescript-conversion branch, there is still a debate regarding TypeScript vs Flow .

[maylukas]

Okay. I changed the base.