Support \relax for author first name abbreviations

[oscargus]

JabRef version: latest dev

Steps to reproduce:

1. Use \relax to specify a two (or more) letter abbreviation of an authors first name, say {\relax Ch}ris Kross
2. Instead of Kross showing up in the author column of the main table, it now says something like relax Kross

A simple (and ugly) way would be to just add relax as a known latex command that is replaced with an empty string. However, it would be nice if the author formatters fully support this notation, leading to that the author is written as Ch. Kross when abbreviated first name is used.

[oscargus]

Relates to #1499

My guess is that using the BibTex name formatter should solve most of these problems.

[oscargus]

Fixed (or rather re-enabled) in #1755.