Rename ArbanJJL to ArbanJB to match composers.dat and Arban_first.ly

Piece Arban_first references composer **ArbanJB**
The composers.dat entry for this composer is **ArbanJB**
But the file is located under **ArbanJJL**

I noticed that the full name is,

**Joseph Jean-Baptiste Laurent Arban**

IMSLP uses simply **Jean-Baptiste Arban**, as does [wikipedia](http://en.wikipedia.org/wiki/Jean-Baptiste_Arban) in its main title, so I opted for renaming the folder to **ArbanJB** and, if desired, we can change the descriptive name associated with **ArbanJB** to the full name.