Add finish time to dashboard; show requests in a more intuitive order

[AndrewEckart]

This PR contains a few updates to the dashboards:

• A new column for finish_time
• Requests are now sorted in (finish_time desc, submit_time desc) order. This is more intuitive: any ongoing requests are shown at the top (latest first), with completed requests appearing after that (most recently completed first).
• Styles have been tweaked a bit

Fixes #114

[codecov[bot]]

Codecov Report

Merging #121 (edd7d29) into develop (73d2f27) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #121   +/-   ##
========================================
  Coverage    91.07%   91.07%           
========================================
  Files           48       48           
  Lines         1334     1334           
  Branches       110      110           
========================================
  Hits          1215     1215           
  Misses         106      106           
  Partials        13       13           

Impacted Files	Coverage Δ
servicex/web/global_dashboard.py	100.00% <ø> (ø)
servicex/web/user_dashboard.py	100.00% <ø> (ø)

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