Change Tile -> toTDF in igvtoolsgui
Switch all uses of SeekableStreamFactory -> IGVSeekableStreamFactory
Implement IGVSeekableBufferedStream
Partial rollback of commit 699df0bc8c690fde7073752d148dd7759f100baf
 (Modify bigwig and bigbed readers so they open and close streams as needed, instead of leaving them open. add tests).
Add dispose() method to Track and DataSource.  Purpose is to release any resources (e.g. file handles) allocated exclusively to respective object.   Method is called upon track removal and application shutdown.  Implemented for BigWigDataSource to close file.
Have CoverageCounter only output comments/track line at beginning of wig file

Previously we were outputting lines like:

track type=wiggle_0
#columns: pos, count

at the beginning of each chromosome.

Now we do that only at the beginning of the wig file, and the #columns line is only output if it's not standard wig
Fix minor bug in IGVSeekableBufferedStream
Added test files
IGV-1966.  SVG output bug (encoding was not set)
Bug checking file extension for type
Improve the script igv.sh

* Add a shebang `#!/bin/sh`.
* Support symlinking the script with `readlink $0`.
* Properly quote the arguments to allow special characters
  by replacing `$*` with `"$@"`.
* Replace the shell process by using `exec`.
* Put the process in the background with `&`.