Add description and documentation and reorganize text styles

[elioqoshi]

Currently our text styles seem a bit incoherent in their organization:

i.e:P, H4 and H5 are not grouped and I am not sure if this encompasses all sorts of text styles we are using in production, there should be more, no?

Also, each text style is missing documentation or a description which would be useful to offer further context when this text style should be used.