Add Styling to the HTML Pages

[afshin]

Fixes #271

Copies more the templates and styling from notebook, including the use of bootstrap.

Including bootstrap adds an npm build step and brings the package from 275kB to 405kB.

[codecov-io]

Codecov Report

Merging #452 (b96ed8e) into master (abaa8cd) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #452      +/-   ##
==========================================
- Coverage   77.78%   77.77%   -0.02%     
==========================================
  Files         106      106              
  Lines        9103     9103              
  Branches      971      971              
==========================================
- Hits         7081     7080       -1     
  Misses       1674     1674              
- Partials      348      349       +1     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/handlers.py	58.24% <0.00%> (-0.27%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update abaa8cd...b96ed8e. Read the comment docs.

[blink1073]

Thanks!