Initial version of slideshow block redesign

Added redesigned slideshow block (closes #527) - 

* Fixed size slideshow (slideshow images are parsed on load and heights are balanced)
* By default, truncated caption (of one line length) are shown. On hover, full caption are expanded above the image
* Slideshow images are vertically aligned to the bottom
* No dependencies on bootstrap carousel
* Auto play/pause and sliding interval are configurable

![slideshow-block-redesign-01](https://cloud.githubusercontent.com/assets/302258/2639525/3f5c9ae6-becb-11e3-8004-cde0469b2acd.png)
![slideshow-block-redesign-02](https://cloud.githubusercontent.com/assets/302258/2639526/3f5d713c-becb-11e3-834f-6d9e3231383f.png)