pageChanged added and replaced with events.pageChanged

[Abhir-24]

As mentioned in the issue, the pagechanged has been added in events.js and in all other files pageChanged has been replaced with events.pageChanged. This issue solves #460

[codecov]

Codecov Report

Merging #658 (7a63344) into master (7096e01) will decrease coverage by 0.24%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #658      +/-   ##
==========================================
- Coverage   66.84%   66.60%   -0.25%     
==========================================
  Files          35       36       +1     
  Lines        3876     3890      +14     
  Branches      747      745       -2     
==========================================
  Hits         2591     2591              
- Misses       1029     1039      +10     
- Partials      256      260       +4     

Impacted Files	Coverage Δ
src/js/BookReader/events.js	100.00% <ø> (ø)
src/js/plugins/search/view.js	48.43% <0.00%> (ø)
src/js/BookReader/Mode2Up.js	56.19% <32.14%> (-2.94%)	⬇️
src/js/BookReader.js	69.73% <88.88%> (-0.08%)	⬇️
src/js/BookReader/ImageCache.js	95.45% <95.45%> (ø)

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[Abhir-24]

@iisa can u pls help me out that what is going wrong in my PR?