Tags and tag searching

[niwakame]

Issue contains the following subissues

• use tags on blog post pages to search for posts containing similar posts
• implement a simple tag search page (tumblr supports searching for a single tag only, anyways)

[funkycode]

I think at the begining it would be more logical to make tags only clickable on posts, so they would display search for the clicked tag. And use search as search only, but in future to make it optional to search thru tags as well.