Add page to list all translations

[oriolbcn]

Closes #47 (only the list part)

Added a separate page that lists all translations found in the repository. Translations are handled in the front-end using Vue.

Why Vue?

Initially using Vue seems to be overkill, but I think it's the best alternative taking into account that we want to be able to search phrases and it should be fast.

These are the options I have considered:

• Load all the translations from the back-end and search from the back-end: This would make the search slow as every time we would need to make a request and load all the translations (which is slow)
• Render all translations from the back-end and then build the search in front-end: This would be tricky as we would need to iterate over all the elements in the DOM to know their key and value and then build a JS object with that to be able to search. Also it would be tricky to show / hide the elements in the DOM when searching. This, further, limits the possibility of doing front-end pagination since the page can get heavy when there are a lot of phrases (therefore a lot of elements in the DOM)
• Do everything in front-end manually (without Vue): This is quite complex as we need to template each of the elements in the DOM and iterate / repaint them when the search changes.

In the end, Vue is a light-weight dependency (80Kb minified), it's similar to the size of JQuery and it allows to implement the front-end rendering in a very elegant and powerful way. So I think it's the best alternative.

Other thinngs

I have moved all the CSS into a separate file and changes the _translate_menu partial to reference that.

By using Vue we need to duplicate all repository partials to use the Vue syntax. The idea is to migrate also the sidebar menu to Vue, therefore eliminating the duplication.