Added possible alternation between slots and prop content to arrows

[w-etc]

• User can now fill slots for prevArrow and nextArrow.
• If both props and slots are introduced to the component, slots will take priority.

This was introduced because we wanted to use custom components as arrows, which the current prop for that would not let us achieve.

[codecov-io]

Codecov Report

Merging #102 into master will increase coverage by 0.84%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
+ Coverage      78%   78.84%   +0.84%     
==========================================
  Files           1        1              
  Lines          50       52       +2     
  Branches       15       15              
==========================================
+ Hits           39       41       +2     
  Misses          7        7              
  Partials        4        4

Impacted Files	Coverage Δ
src/components/Paginate.vue	78.84% <100%> (+0.84%)	⬆️

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