Changed favicon to png

[Mipronimo]

closes #1420

[codecov]

Codecov Report

Merging #1421 into master will increase coverage by 0.1%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #1421     +/-   ##
=========================================
+ Coverage   96.78%   96.89%   +0.1%     
=========================================
  Files         144      144             
  Lines       17185    17564    +379     
=========================================
+ Hits        16632    17018    +386     
+ Misses        553      546      -7

Impacted Files	Coverage Δ
privacyidea/lib/tokens/hotptoken.py	100% <0%> (ø)	⬆️
privacyidea/lib/apps.py	100% <0%> (ø)	⬆️
privacyidea/lib/utils.py	98.36% <0%> (+2.43%)	⬆️

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