Feat/swagger auth

[Dawn0472]

add swagger authorization

1. add auth button in swagger
2. add auth url to get token (逾7天更新一次，若無token則新增，有token直接取得- one user vs one token)
3. update core.models.Token(預設 one user vs multiple token)
4. update BearerAuthentication function(swagger authorization)
5. update api import BearerAuthentication

[josix]

Hello @Dawn0472, thank you for working on this. There are some coding style issues, could you help me fix it, thanks!

[codecov-commenter]

Codecov Report

Patch coverage: 65.82% and project coverage change: +0.01 🎉

Comparison is base (4b520ac) 69.56% compared to head (287fc55) 69.57%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1141      +/-   ##
==========================================
+ Coverage   69.56%   69.57%   +0.01%     
==========================================
  Files          82       87       +5     
  Lines        3364     3444      +80     
==========================================
+ Hits         2340     2396      +56     
- Misses       1024     1048      +24     

Impacted Files	Coverage Δ
src/core/models.py	95.71% <ø> (-0.49%)	⬇️
src/users/api/views.py	36.66% <36.66%> (ø)
src/pycontw2016/urls.py	84.21% <66.66%> (-1.51%)	⬇️
src/core/authentication.py	81.25% <79.31%> (-18.75%)	⬇️
src/attendee/api/views.py	42.85% <100.00%> (ø)
src/events/api/views.py	52.00% <100.00%> (ø)
src/sponsors/api/views.py	41.17% <100.00%> (ø)
src/users/api/urls.py	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes

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