Headings feature

1. The data should be loaded with three headings and one paragraph.
2. Put selection inside each block and check if dropdown label is changing properly.
3. Play with headings:
   • Switch headings using dropdown.
   • Apply same heading twice to same block to see if its switching with paragraph.
   • Put selection that spans across multiple blocks and switch headings.
4. Enter behavior alternations:
   • At the end of a heading should create a new paragraph.
   • In the middle of a heading should split it.