[WIP] Simplifying CSS
#54, #56 General rewrite of the CSS code
#62 Introducing LoadedChapter
#62 Refactoring LoadedChapter into ChapterContents
#62 <link>/<script> injected by ChapterContents is now annotated with an id
#62 ChapterContents now doesn't hardcode the page at which we enter the chapter
#62 Caching instances of ChapterContents
#65 WIP
#65 WIP (it works)
#65 Opening books from a Library object
#68 Placeholders in the top menu
#70 Setting maximal size for images
#66 If we can't change chapter, return to the current page, reinitialize keys
#67 Adopting stylesheet without padding for Firefox OS 2.1
#67 Typo fixup
#72 Margins on Firefox OS
#73 Same CSS everywhere
#73 Same CSS everywhere, part 2
#73 Cleanup
#50 BookViewer.prototype.close