Pass header object to TiddlyWiki.toHtml() instead of header name

Twee was trying to pass the header object while TiddlyWiki expected
a header name, which means Twee didn't work.

This solution is simpler than the alternative (making Twee pass the
header name), since it reduces the coupling between the App object
and TiddlyWiki.
Rename TweeApp.targetsPath to builtinTargetsPath

This is the name that TiddlyWiki expects.
Removed getPath() method and scriptPath field

There were no calls to getPath(). And after removing getPath(),
scriptPath was only used in a single method per class, so it could
be replaced by local variables.
Merge pull request #121 from mthuurne/twee_header_fix

Header-related fixes for Twee
Quick OS X path bugfix

Now, app.scriptPath points back to /Contents/Resources inside the app bundle.
Whitespace cleanup

* Converted all the .py files back to spaces instead of tabs.
* Slightly tweaked StoryInit's execution to run as late as possible, and
to not run when restoring the game from a bookmark.
New StorySettings dialog

* The StorySettings passage is now edited in a special GUI dialog, with
checkboxes and textboxes corresponding to each entry.
* The settings for this StorySettings dialog are now stored in the
Header class, in the form of a list of dictionaries. Thus, custom
headers may use different StorySettings entries, if they wish. See
Header.py to examine the current format used for this data.
* Header class: renamed files_to_embed() to filesToEmbed(), primarily
because snake_case just isn't Pythonic(TM).
* Also, the filesToEmbed list now requires that a path be specified,
instead of assuming it's in the format's home path.
* The __init__ method of Headers now takes a third argument:
builtinPath, which should always refer to the path used by the built-in
story formats.
* Added a Help menu to the passage editor, linking to a few wiki
articles concerning passages.