Streamline and parallelize Wave effect

[ferdnyc]

You know the drill by now. Main for() loop decorated with #pragma omp parallel for, and streamlined for cleaner parallelization.

In this one I also eliminated an unnecessary copy of the frame image data, taking advantage of QImage's implicit data sharing and automatic copying functionality to use the frame image's constBits() as the source pixel data, and (an implicitly-copied) bits() as the destination.

11-second Big Buck Bunny clip export time on my 4-core system: 28s, down from 1m24s (nearly 3x as fast).

[codecov-io]

Codecov Report

Merging #425 into develop will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff            @@
##           develop     #425   +/-   ##
========================================
  Coverage    42.37%   42.37%           
========================================
  Files          129      129           
  Lines        13276    13276           
========================================
  Hits          5626     5626           
  Misses        7650     7650

Impacted Files	Coverage Δ
src/effects/Wave.cpp	0% <0%> (ø)	⬆️

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[jonoomph]

LGTM! Nice work!