Improves the categories.html templates

This is just a suggestion, but I thought the categories page could look
nicer.
Contributing guidelines enhanced
Contributing guidelines enhanced some more
Added Links to sidebar, fixed Github repos, fixes #44
JS optimization
Merge branch 'categories' of https://github.com/magnunleno/pelican-bootstrap3 into magnunleno-categories

* 'categories' of https://github.com/magnunleno/pelican-bootstrap3:
  Improves the categories.html templates
Prettified tags as well
Fixes pages titles

Is a good SEO practice to unify the pages titles and always reference
the site name. Ex: "My Awsome Article - My Own Blog" or  "My Awsome
Article | My Own Blog"
Adds some improvements in Open Graph

Adds the following tags in open-graph: og:site_name,
article:published_time, article:section and article:tag
De-global padding of font-awesome icons.

Padding all font-awesome icons to the right on a site-wide basis means we
can't have unpadded icons anymore. We change this to a label class that has
the identical margin to the left.

Also, for some icons, we simply use a space, because the full spacing seems
excessive.
Some basic styling for figures and their captions.
Added custom css option
Merge pull request #51 from magnunleno/pages-titles

Fixes pages titles
Merge pull request #53 from hlapp/figure-styles

Some basic styling for figures and their captions.
Merge pull request #52 from hlapp/icon-label-spacing

De-global padding of font-awesome icons.
Authors are important
Update CONTRIBUTING.md
Break long word in sidebar.
Move .wordbreak into #sidebar.
Move sidebar sublist into nested lists. Fixes #47.