thoughts about new record-crate design

@DeviaVir I'd like to preface this post with the fact that I think that the new Polymer layout is looking awesome, things look 100x more professional than my first pass at the design.

Here's some thoughts I have that would get me using record-crate as part of my DJing workflow:

**Listing Page (record-crate-page?):**
- the `bpm` on the crate page dominates a bit, and it's not immediately clear to me that it is the `bpm`:
- now that we're indexing the creation date of the file (https://github.com/bcoe/record-crate/commit/92dea0e325458783e1659719a4a82d6d72eb0c19) it would be great to also have this on the listing page., perhaps downplaying the `bpm` a bit and labeling it.
- on the main listing page (the `crate` page?), it's a bit hard to tell the divisions between the different tracks. It might be good to vary the background-color slightly between each track.
- when clicking on a track and viewing the `info-page`, it's frustrating that hitting `back` or `ESC` does not take you back to the same position in the list of songs you were scrolling through (it always takes you back to the top). It would be great if we kept track of your list position and scrolled back to this position, whenever back is hit.
- As discussed here, https://github.com/bcoe/record-crate/pull/18 I think search should be one of the primary ways you interact with your music-collection.

**Info Page:**
- It would be awesome if we could add the concept of `tags` back on this page, this is a feature I'd like to have for bookmarking various tracks in my music collection.
- there are some layout issues surrounding the back button:

- It would be awesome if there was an option on this page to add the track to a collection other than `All`, perhaps we should use the terminology `Crates` for this?
- perhaps this organization feature could be offered on the main-listing page too?
- when we're ready to start implementing this feature, I'll do the back-end logic for grouping tracks within ES., we can use a feature similar to tags, and restrict search-results by `Crates`.

**On the topic of pagination:**

When playing a gig, I often find myself leafing through large swaths of my music collection looking for the next track to throw on. If we add pagination functionality, it would be great to keep this as seamless as possible -- perhaps have something like infinite scrolling.

Phew, these are all my thoughts for the time being! I'm excited about the progress we're making. `record-crate` is close to the app I personally need for wrangling my music-collection while playing live sets.

Start by reviewing the `record-crate-page`, `crate`, and `info-page` entry points, along with the search discussion in pull request #18. This issue covers several independent UI, navigation, tagging, crate, and pagination ideas, so split it into focused tasks before implementation. Done should be defined separately for each selected behavior and verified in the affected pages.

Written by the indexing model from the issue text.