Added the setter to update the flatSegmented items

In this PR I have:
1. Updated the library code style
2. Updated the way how items are passed. Instead of using a dictionary you can pass now an array of `PPiFlatSegmentItem`with title and icon.
3. Added setter to set items after control initialization ( to fix this issue https://github.com/pepibumur/PPiFlatSegmentedControl/issues/18 )