use section name instead of section ID in tag page <title>

As per content pages use the section title instead of the section ID on tag pages.

Before 
![screen shot 2014-10-16 at 17 22 17](https://cloud.githubusercontent.com/assets/1764158/4666192/352d13b2-5551-11e4-81b7-7956b0f54646.png)

After
![screen shot 2014-10-16 at 17 25 13](https://cloud.githubusercontent.com/assets/1764158/4666194/39d1357e-5551-11e4-94a4-2dec25c07f0f.png)


Maybe rename the `section` property `sectionId` to make the distinction clear?