Lock touch direction to avoid change on scroll

[naikipl]

Fixes #308

The onStart trigger is moved from onTouchStart to onTouchMove because we need to act on drag direction. The goal being: If the first touch move is in the correct slider direction, trigger onStart; Otherwise, ignore further dragging.

Added onTouchEnd for cleanup.

As a result, the following user actions will no longer move a slider:

• touching the track
• dragging a horizontal slider vertically
• dragging a vertical slider horizontally

[codecov]

Codecov Report

Merging #580 into master will increase coverage by 0.81%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #580      +/-   ##
========================================
+ Coverage   95.18%    96%   +0.81%     
========================================
  Files           2      2              
  Lines          83    100      +17     
  Branches       25     31       +6     
========================================
+ Hits           79     96      +17     
  Misses          4      4

Impacted Files	Coverage Δ
src/utils.js	95.69% <100%> (+0.96%)	⬆️

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[yoyo837]

Rebase please.