Tons of changes

Added the ability to right click.
Added the Settings window to try out what you could do with right click.
Big changes in the code: global object that contains everything (better
encapsulation, avoids random global variables like ALL_WINDOWS which
isn't interesting for the user).
Changing the API's name to Please.
Bug correction:
- closing windows that would close other ones (because of bad event
handling)
- click on window wouldn't focus
- right click on button would focus on the window

CSSParser isn't working, nor is HTMLParser (I haven't tested it quite
yet)