Remove module "TuxGuitar-viewer"

This module looks like an attempt to reincarnate base TuxGuitar module
in some "better" or "smaller" form. But it fails to completely replace
the parent. This child inherits too much sins, and too litle dignity.

I think it would be too hard for me either to keep two slighlty
different TuxGuitar instances or to merge them back into the one module
(the hardest part is to detect each change that should be merged, and
how should it be done). Therefore I sentence this ugly orphan to quick
and painless death.
Remove whitespaces at EOL

Whitespaces are completely amusing. I know that such kind of change
create a kind of mess in the project history, BUT it looks much better
without stupid spaces-at-eol. Empty lines must be empty.
Replace custom TGLock class with ReenterantLock

TGLock class should be removed because generic (and error-prone) Lock
implementation already exists in JVM 1.5+.

Also it is recommended to use try-finally block when Lock is used to
make sure that lock is unlocked even when an exception occurs inside
block.

There are two pitfalls found during the fix:

 * try-finally block is not implemented in TGShareSong class, because
   lock and unlock are used in different methods (and I didn't have much
   time to find where try-finally should be placed in that case)
 * There are found several checks that are not really thread-safe.
   Anoter thread can acquire the lock between isLocked() and lock()
   calls. We must replace these if's with more proper solution
Code cleanup in MidiPlayer class

 * fix javadocs
 * remove unused methods
 * possibly memory leak found