Add QTimer to ensure background jobs are scheduled correctly.

[m3nu]

Fixes #777

[codecov-io]

Codecov Report

Merging #780 (1eb37b5) into master (227e06d) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #780      +/-   ##
==========================================
+ Coverage   73.50%   73.58%   +0.07%     
==========================================
  Files          53       53              
  Lines        3590     3593       +3     
==========================================
+ Hits         2639     2644       +5     
+ Misses        951      949       -2     

Impacted Files	Coverage Δ
src/vorta/scheduler.py	70.27% <100.00%> (+2.67%)	⬆️

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