Lazy Load and Tiled Galleries/Photon interop and some other enhancements

This PR has some improvements to both the code and functionality of Tiled Galleries along with a few changes in Photon.

* The first and foremost purpose of the PR is to improve the interoperability of lazy loading (via some whatever plugin, e.g., the official Lazy Load plugin) and Tiled Galleries. To get there, some changes had to be made to how the tiles are placed and how their size is reserved. You should find all the information in the commit messages. Important fixes include proper behaviour when refreshing pages (not force refresh) when the official Lazy Load plugin is activated in Firefox, IE and Safari as well as dropping the need to eagerly load Tiled Gallery containers (as is done in the official plugin). To test this out, I created a small lazy load [plugin of my own](https://github.com/rase-/WP-jQuery-Lazy-Load).

* The aforementioned changes also took care of another issue that I reported earlier to happen on Chrome: https://github.com/Automattic/jetpack/issues/476 and would in theory allow for Tiled Galleries to work without Photon as well.

* It looks like Tiled Galleries don't work too well in IE 10 (don't resize and totally explode in Widgets). They seem to work just fine after the changes made here, though.

* Interoperability of lazy loading and Photon was also enhanced: images not in a tiled gallery would not be displayed properly when Photon was enabled before.

* A regex in Photon that strips the `height` and `width` attributes from images would strip attributes like `data-original-width` into `data-original-`. This regex now only strips the `height ` and `width` attributes by making sure there is a whitespace before the stripped matches.

So that the rectangular Tiled Galleries look great (row margin is too wide consistently, which only happens on occasion in master), this PR needs to be merged as well https://github.com/Automattic/jetpack/pull/500.

What do you think of the changes? Ideas for improvement?