Update about page informations

* add Giorgia Marenda (@gmarenda)
* fix intro
* remove link to jquery-pixel library (moved to main repo)
Fix gallery path

Gallery is a shared partial used in different views and a gallery path must
be specified in order to get correct pagination links.
Add tool tips; add keyboard shortcuts; main PIXEL library refactoring

* add tipsy tool tips library
* add editor tool tips, closes #45
* add tool tips toggle checkbox
* add keyboard shortcuts, closes #38
* invert "+" (add frame) and "-" (remove frame), closes #46
* fix `clearAll` method
* fix code style issues (use camel case for js variables)
* remove `frames` counter variable
* remove main canvas bitmap (use only `frames` array)
* remove deprecated code
* add `Bitmap` class
* add `toObject` method