Display imported files in alphabetical order

[angsch]

Fixes the order of the file names in the title bar

[codecov-io]

Codecov Report

Merging #426 (175ce8f) into main (503ba8f) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #426   +/-   ##
=======================================
  Coverage   72.05%   72.05%           
=======================================
  Files          10       10           
  Lines        2637     2637           
=======================================
  Hits         1900     1900           
  Misses        737      737           

Impacted Files	Coverage Δ
pdfarranger/pdfarranger.py	66.46% <100.00%> (ø)

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