Eliminate duplication of character replacement in k3bpatternparser

All of the string fields used the same character replacements, so define a function that handles that and call it instead of copy- pasting code.

In !21 (merged), it was suggested that I replace the code duplication with a static floating function. C++ isn't my strongest language and my google-fu failed me as to exactly what a floating function was, so if I didn't do this correctly, please let me know and I will fix it.