Typography has incorrect theme presets

[FranBran]

The variants of typography defined in the theme don't match those of https://material.io/design/typography/#

(e.g. the font-size of body1 should be 1rem instead of 0.875rem, etc.)

• This is a v1.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Your Environment

Tech	Version
Material-UI	v1.4.2
React
browser
etc.

[oliviertassinari]

@FranBran You are right. We will batch some breaking changes with v2. I think that we can release such version by the end of 2018.