Annotation passages

Annotation passages are non-playable passages that hold text to display
on the story map, to annotate, comment or document the source code of
the game. They have a different colour and size to normal passages.
Added lastlink() function

This function returns the text of the last passage link clicked. It can
be used to determine exactly which link was clicked to reach this
passage. I think it fulfills some of the basic use-cases that the
currently unimplemented "click-and-set" links have, without necessarily
needing to introduce a variable.
Fixed line breaks in annotation passages

Annotations' text on the story map now contains line breaks.

Also added support for lastlink() to <<actions>> and <<return>>.
Amended 'New Passage Here' right-click menu

The right-click menu now has "New Stylesheet", "New Script" and "New
Annotation" included.

Also fixed a story map word-wrap bug.
Some small IDE fixes

* Drag-and-dropping text now moves the text instead of copying it. The
'drag-and-drop to link to new passage' functionality, however, remains
unchanged.
* Undoing the 'drag-and-drop to link to new passage' now undoes both
pairs of inserted brackets, and not just one.
* Opening a passage whose editor window is open but minimised with now
un-minimise the passage.
* Test Build will no longer fail if the story's save destination is set
but doesn't exist (by, e.g. transporting the .tws to another computer).
Added font embedding

Since fonts are really only useful to CSS, they're imported as
stylesheet passages containing the font file in base64 encoding.

Sadly, I don't think it's possible for wxPython to load the fonts and
display a proper font preview pane for each of them...
Default text for new stylesheets

* New stylesheets now contain a template showing the three most common
selectors (body, passage, link).
* Added SVG as a font file type.
* Added embedded font support for the obsolete <font> element, just in
case someone really needs it.
* Tooltips now display full passage titles as well as tags and text.
Moved format-specific code to separate files

The format-specific engine code for Jonah and Sugarcane has been moved
out of the "header.html" files into "code.js" files within each targets
subdirectory. Also, Responsive now transcludes Sugarcane's code into
itself, saving the need to maintain two copies.

Also, decided to reconsider and remove lastlink(), for at least the
moment.
Some bugfixes

* Fixed bug where embedded images wouldn't work in tagged stylesheets.
* Fixed bug where the "Add new stylesheet" right-click menu item wasn't
working.
* Converted sugarcane/code.js tabs to spaces
* Added the Jonah and Sugarcane code.js files to buildexe.py
Merge pull request #88 from webbedspace/master

More changes