Refactor typestate configuration into enums

[bugadani]

VerticalOverdraw and HeightMode: #112

[rfuest]

Just to provide some feedback on the API from a user perspective: When I tried to change an example to be vertically centered I wasn't able to do this without looking at the docs. I could easily find the vertical_alignment method in TextBoxStyleBuilder by using code completion, but I had no idea that I could use the same CenterAligned type for both vertical and horizontal alignment.

[bugadani]

Were the options otherwise easy to discover?

I understand why this can be somewhat difficult and I would like to replace it with a better solution. Originally, I decided on CenterAligned implementing both orientations so that I don't have to use the same name for two different objects, and also avoid having to spell out the module. Maybe a sensible solution would have been to call horizontal CenterAligned and vertical MiddleAligned but I'm not sure. At any rate, refactoring to two distinct enums will fix this.

[rfuest]

I only wanted to change this one and haven't paid much attention to the other options. But all options that use types instead of enums will have similar problems. If you decide to keep using type states I would suggest to list the available options in the docs for the corresponding builder methods.