Make it possible to click tags from article view and global/favorite feed index

[cirosantilli]

Currently on https://github.com/gothinkster/react-redux-realworld-example-app/tree/9186292054dc37567e707602a15a0884d6bdae35 and https://github.com/gothinkster/angular-realworld-example-app/tree/9e8c49514ee874e5e0bbfe53ffdba7d2fd0af36f the only place where you can click to view articles under a given tag is from Popular Tags on the home page.

Tags also show on the following other places:

• from the global/favorite index (/#/) on a given article: clicking it opens the article, not the tag
• when viewing the article itself (/#/article/test-l9ah7). Clicking it does nothing.

Both of those above would be better if they actually opened the list of posts with the tag, otherwise it's quite unintuitive, and I start to wonder if the frontend is broken and have to compare with others :-)

Two off-topic things come to mind:

• automated frontend testing setup in this repo is a must: https://github.com/gothinkster/realworld/issues/269
• it would be better to have corresponding URLs for tags and for global feed, those currently just have the same root url as the global feed