Fix problem with dragging images within TW5

Dragging an image within the same TW5 window was causing a crash
Merge pull request #226 from asampal/master

Style changes in user visible text node -> Node
Trap filter syntax errors

Now a syntax error on a filter just causes the filter to return the
error message as it’s single result.

Fixes #189
Sort out the docs for the tabs macro
Add StephanHradek's new tw5magick site
Change macro attributes to not wikify their content

One consequence of wikifying macro attributes before use was that we
couldn’t have tiddler titles with wikitext syntax in, which was
definitely a problem.
Docs updates
Fix problem with tag-configurable item lists not being able to interleave shadow and non-shadow
Remove special provision for jQuery

This dates from an ancient version of TW5 which had a dependency on
jQuery. Now we’d install jQuery as an ordinary tiddler module, not a
library module.
Stop generating static content when we're saving an encrypted wiki
Add [is[tiddler]] filter operator

For selecting all non-shadow tiddlers, whether or not they are system
tiddlers
Rejig the main save template to get rid of the separate system tiddler area

It dates from an ancient version of TW5, and is really redundant now.
It also meant that system tiddlers were not encrypted, which seems
confusing for end users.
adjust media query to remove box-shadow for small screens. fix some @media indentations
Reorganise the main file saving templates

We’re introducing a mechanism that allows us to decide which tiddlers
get saved. Using `$:/core/save/all` gives all tiddlers, as before.
Using `$:/core/save/empty` gives an empty wiki. Saving an empty wiki
from tw5.com isn’t the same as the empty wiki cooked from
editions/empty because the two editions have different plugins and
other system tiddlers.
Merge pull request #231 from pmario/fix-media-queries

adjust media query to remove box-shadow for small screens. thanks @pmario
Move Google Analytics integration into a proper plugin
Build an experimental empty.html from the tw5.com edition
Add screenshot of tiddlywiki classic
Big green download buttons
Docs updates