Add plot grid and show bad shutdown support.

[roachsinai]

Hi @rfrail3 I made an update for the plot bar chart script.

1. support plot grid, it will be helpful when you what know the start time and end time of a bar split.
2. plot badtime state if an database entry's endst is BAD.

(nn) hmank ~/c/G/tuptime dev » tup -a 1 --lwidth 1.5

If we got an tuptime entry like this:

{'startup': 34,
  'btime': 1553735469,
  'uptime': 4.74,
  'offbtime': 1553735474,
  'endst': 0,
  'downtime': 9497.26,
  'kernel': 'Linux-4.20.17-1-MANJARO-x86_64-with-arch-Manjaro-Linux'},

All time consumed by startup and shutdown state will be added and turn to badtime meas bad shutdown time.

---

usage:

(nn) hmank ~/c/G/tuptime dev » tup -h               
usage: tuptime-barchart.py [-h] [-f FILE] [-b BEGIN_DATE] [-e END_DATE]
                           [-p PAST_DAYS] [--fwidth FIG_WIDTH]
                           [--fheight FIG_HEIGHT] [-w BAR_WIDTH]
                           [--lwidth LINE_WIDTH] [-a GRID_ALPHA]

optional arguments:
  -h, --help            show this help message and exit
  -f, --filedb FILE     database file
  -b, --bdate BEGIN_DATE
                        begin date to plot, format:Y-m-d.
  -e, --edate END_DATE  end date to plot, format:Y-m-d. Default edate is
                        today.
  -p, --pastdays PAST_DAYS
                        past days before edate to plot, will be ignored if set
                        bdate (default is 7).
  --fwidth FIG_WIDTH    figure width.
  --fheight FIG_HEIGHT  figure height.
  -w, --bwidth BAR_WIDTH
                        The width of the bars (default is 0.5).
  --lwidth LINE_WIDTH   line width of figure grid (default is 1).
  -a, --galpha GRID_ALPHA
                        alpha value of figure grid (default is 0).

[rfrail3]

Nice to see how this small change produce more feedback to the user. Good work, thanks!