WebUI tidy-up: Option groupings, updated help text, and user option to determine page size for upcoming/completed/failed recordings.

As the title says, really. Probably easier just to paint a couple of pictures, though.

Only one functional change: the addition of a combobox to the 'Digital Video Recorder' screen so the user can change the length of the list of recordings (upcoming/completed/failed) vs the hard-coded default of 20 per page otherwise.

Everything else is cosmetic: grouping of options into animated, rollable-uppable boxes, some options put side-by-side instead of on top of each other, that sort of thing. Help text formatting updated, some content changed (not material) and embedded images added/updated.

![userselectlistlength](https://cloud.githubusercontent.com/assets/6093716/3074942/29101916-e35b-11e3-9246-b90841d99c59.png)
![generaloptions](https://cloud.githubusercontent.com/assets/6093716/3074946/6cb8b682-e35b-11e3-859e-394f8c1f7482.png)
![timeshiftoptions](https://cloud.githubusercontent.com/assets/6093716/3074963/25595fde-e35c-11e3-8b42-96e5a5f79491.png)
![dvroptions](https://cloud.githubusercontent.com/assets/6093716/3074961/ef8d9d52-e35b-11e3-8f94-b764de128b0d.png)

Discuss.