Add options for toolbar, editor.

[spooker0]

I added a few examples in the storybook:

1. Custom block types. I added h4 and h5 as examples. All the other ones can be added/removed from the menu.
2. Option to hide redo/undo on toolbar.
3. Option to hide block formatting altogether on toolbar.
4. Can disable/enable any plugins on Editor, like the floating format bar. Should solve #57
5. Added option to move subscript, superscript, strikethrough out of the menu into separate icons.