Add category pagination

[josephting]

Resolves #3.

It's my first time working with Gatsby so please let me know if you find anything that need changes.

I tried to add pagination with pagination-ellipsis if number of pages exceeds 7 pages but my JSX experience is lacking as well.

Some styles got overwritten (pagination number had bullets) for some reason so I added some styles to fix the pagination layout.

Pagination Preview

[codecov-io]

Codecov Report

Merging #18 into master will increase coverage by 0.17%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
+ Coverage   94.55%   94.73%   +0.17%     
==========================================
  Files          12       12              
  Lines         147      152       +5     
  Branches       23       24       +1     
==========================================
+ Hits          139      144       +5     
  Misses          6        6              
  Partials        2        2

[boyney123]

Thanks for this awesome work @josephting ! 🎉

I'm in the middle of making a theme to handle multiple sites, so I will hold of this PR for abit to add it to the root theme, so ALL sites can get this feature 👍

Awesome work, thanks very much!

[josephting]

Nice. Feel free to ping me should you need anything from me. 😄

[boyney123]

Nice. Feel free to ping me should you need anything from me. 😄

Yeah will do 👍