feat req: normalize rectangle type between components

[Im-Beast]

What this feature is meaning to achieve
Some components use their own Rectangle implementations, e.g. InputRectangle and TextRectangle.
This creates issues with layouts and some other things.

Solution
Rectangle's should be normalized so that every component uses normal Rectangle. This would mean that some components behaviour should be adjusted to make use of properties it didn't use (e.g. height in Input)

[Im-Beast]

I'll want to do this right after #29 or even in it.