pybootchartgui: Fix the filename and add a default format

pybootchartgui: Fix the filename and add a default format

* Fix teh output filename to make it easy to use
* Add a default output format (svg)
* Fix the usage message
* Fix the version to v1.0.0

Currently, the help messages are:

$ ./pybootchartgui.py --help
Usage: pybootchartgui.py [options] /path/to/tmp/buildstats/<recipe-machine>/<BUILDNAME>/

Options:
  --version             show program's version number and exit
  -h, --help            show this help message and exit
  -i, --interactive     start in active mode
  -f FORMAT, --format=FORMAT
                        image format: svg, pdf, png, [default: svg]
  -o PATH, --output=PATH
                        output path (file or directory) where charts are
                        stored
  -s NUM, --split=NUM   split the output chart into <NUM> charts, only works
                        with "-o PATH"
  -n, --no-prune        do not prune the process tree
  -q, --quiet           suppress informational messages
  --very-quiet          suppress all messages except errors
  --verbose             print all messages

[YOCTO #2403]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>