320/bug/autoplay e2e fails

[giacomo-cgn]

Closes #320
Random delay between flipping the book cover and the first page caused unexpected test failures.
Added longer wait time to cover for these randoms delays (before it was assumed that delay was always 0)
From: 3000ms -> 2% fails (original)
to: 4000ms -> 0% fails

[codecov]

Codecov Report

Merging #344 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #344      +/-   ##
==========================================
- Coverage   60.83%   60.78%   -0.06%     
==========================================
  Files          32       32              
  Lines        3409     3409              
  Branches      646      646              
==========================================
- Hits         2074     2072       -2     
- Misses       1071     1073       +2     
  Partials      264      264              

Impacted Files	Coverage Δ
src/js/plugins/tts/WebTTSEngine.js	65.41% <0.00%> (-1.51%)	⬇️

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[cdrini]

Code lgtm! Could you rebase? That should fix travis :)