Adding translation team logos

This upload provides both an .svg and a high resolution .png of translation team-specific data.table logos. The differences between the main logo and translation team-specific logos are the inclusion of a two- to four-letter language code as superscripted text at the end of the package name within the logo.  [Full code list here](https://en.wikipedia.org/wiki/List_of_ISO_639_language_codes). I used lowercase letters since this seems most common with these codes.

I am not sure if more specific country-based versions of the language codes are needed for any of the teams (the four-letter versions of the codes, [see list here](https://www.andiamo.co.uk/resources/iso-language-codes/)). I've made one for the Brazilian team, based on recent discussions (file name ending with "ptbr"), which provides a nice example of what this would look like.

Please let me know if any general changes are needed and if additional, country-specific language code versions would better serve any of the teams.

Author: jmrung