Allow one hot encoding for dataframes, for all categorical columns

[SamVanhoutte]

if the column name is not passed, would be good to scan the dataframe for all categorical columns and one-hot encode them

[SamVanhoutte]

Extra information:
A categorical column is a column that contains text values. As for machine learning, all values have to be translated into numeric values, the concept of one-hot encoding is applied. That concept is easily explained with the picture below.

So, this issue could be seen to implement a function that takes all text-columns of a dataframe and one-hot-encodes them.