Sequence, comment counts, header

1) Sequence: If an element has a `data-link-context` attribute, this'll specify the endpoint for retrieving the swipe sequence for any child links of that element. Allows overriding of the default behaviour of using `/front-trails/{section name}` with the section extracted from link url.

2) Comment counts: hashes on urls are maintained in swipe-on-click, which fixes loading of comments after a click on a front comment count. 

3) Header positioning: fixes occasional glitch that places header over content