ENH: Include dtypes in DataFrame repr column headers
In R notebooks and consoles, dtypes are included below column names in plain text and rich renderings of data frames/tibbles (see images below). This is quite helpful in identifying the data type of a column without having to call df.dtypes or df.info(). Is there any appetite for introducing a similar mechanism for the plain text and HTML reprs of Pandas DataFrames?

**R notebook**
![r_notebook](https://user-images.githubusercontent.com/4974928/35398775-a99152f6-01ea-11e8-8988-aab06d7e66d1.PNG)

**R console**
![r_console](https://user-images.githubusercontent.com/4974928/35398777-a9ba8806-01ea-11e8-8513-027483c79b60.PNG)



