Prevent bats/flakes from overlapping QR-codes

[jonasKjellerup]

Addresses issues #303.

• Sets relative positioning and z-index of QR-codes on the user/pay page.
• Tested for bats, beerflakes, and snowflakes.

[codecov-commenter]

Codecov Report

Merging #315 (2b015ff) into next (35d32f9) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             next     #315   +/-   ##
=======================================
  Coverage   83.07%   83.07%           
=======================================
  Files          31       31           
  Lines        2659     2659           
  Branches      188      188           
=======================================
  Hits         2209     2209           
  Misses        418      418           
  Partials       32       32           

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[VirtualSatai]

Would be more fun to always have a bat in the QR code, but it not fucking it up because of the redundancy allowed in QR codes. Anyway, this LGTM

[falkecarlsen]