Incorrect handling of parentheses in TQVectorAuxObservable

As initially reported here: #234 (comment 2775174) the splitting of arguments for the VecAT operation mode does not work correctly. Looking briefly through TQStringUtils it seems that TQStringUtils::split by virtue of TQStringUtils::findParenthesisMatch allows the opening and closing parenthesis passed as arguments to be multi-character sequences instead of forming pairs.

• This may be intended but should be documented more cleanly in the comments of split and findParenthesisMatch.
• For the original problem at hand we can simply switch to TQStringUtils::tokenizeVector which only differs little in terms of usage/signature but does achieves the desired behavior.