Docs: Add short links on the pages that have them

Some presentation had direct links to the newcomer guide.

We have some "URL shortener":

https://coala.io/newcomer -> http://docs.coala.io/en/latest/Developers/Newcomers_Guide.html

https://coala.io/new -> https://github.com/issues?utf8=%E2%9C%93&q=is%3Aopen+is%3Aissue+user%3Acoala+label%3Adifficulty%2Fnewcomer++no%3Aassignee

etc...

We should add the URL shortened link on the page getting shortened in the documentation; so people browsing around the docs know there's a short URL pointing to the page.

URLS:

```
location /newcomer { return 302 http://docs.coala.io/en/latest/Developers/Newcomers_Guide.html; }
location /newcomers { return 302 http://docs.coala.io/en/latest/Developers/Newcomers_Guide.html; }
location /new { return 302 https://github.com/issues?utf8=%E2%9C%93&q=is%3Aopen+is%3Aissue+user%3Acoala+label%3Adifficulty%2Fnewcomer++no%3Aassignee; }
location /low { return 302 https://github.com/issues?utf8=%E2%9C%93&q=is%3Aopen+is%3Aissue+user%3Acoala+label%3Adifficulty%2Flow++no%3Aassignee; }
location /review { return 302 https://github.com/pulls?q=is%3Aopen+is%3Apr+user%3Acoala+label%3A%22process%2Fpending+review%22+sort%3Acreated-asc; }
location /languages { return 302 https://github.com/coala/bear-docs/blob/master/README.rst; }
location /chat { return 302 https://gitter.im/coala-analyzer/coala; }
location /git { return 302 http://docs.coala.io/en/latest/Developers/Git_Basics.html; }
location /commit { return 302 http://docs.coala.io/en/latest/Developers/Writing_Good_Commits.html; }
location /cep { return 302 https://github.com/coala/cEPs/blob/master/cEP-0000.md; }
location /tutorial { return 302 https://docs.coala.io/en/latest/Users/Tutorial.html; }
location /writingbears { return 302 https://docs.coala.io/en/latest/Developers/Writing_Bears.html; }
location /channels { return 302 https://github.com/coala/coala/wiki/Communication-Channels; }
location /newform { return 302 https://docs.google.com/forms/d/e/1FAIpQLSd7g_MU_c-BMQ62WHeznrvcoXwqW87O_Wq4Gz7-pp8PJ38Wdg/viewform; }
location /projects { return 302 https://github.com/coala/coala/wiki/Project-Ideas; }
location /reviewsprint { return 302 https://docs.google.com/forms/d/e/1FAIpQLSd4vHafTyY4RW--fOyIVecBM0WKNEeF-RyFvUn83jCF9ou2tg/viewform; }
location /reply { return 302 https://github.com/coala/coala/wiki/Reply-Templates; }
location /linespots { return 302 https://gitlab.com/sims1253/Linespots; }
location /usability { return 302 https://docs.google.com/forms/d/e/1FAIpQLSe9lZxuYEKlvxXzQUOTwrre3CQMNsks7eOzEl49_2q5vlDl0w/viewform; }
location /cep5 { return 302 https://github.com/coala/cEPs/blob/master/cEP-0005.md; }
location /starwars { return 302 https://www.youtube.com/watch?v=JWVCMjKU_10; }
```