Update to latest version of normalize.css and fix tab styling

Tab styling was inconsistent on Firefox due to some line-height issues.
Update link to tags docs
Left off previous commit
Fix setTextReference()

It wasn’t working for non-existent tiddlers. Also added support for
setting indexed properties of a data tiddler.
Extend tag manager to edit icons assigned to tags

Add a dropdown for choosing available images for a tag.

As part of this change we need to tag tiddlers that contain images
typed as wikitext (these are inline SVG icons) so that we can display
them in the dropdown.
Tweaks to list-before and list-after field descriptions
Default colour tweaks
Add support for tw-home message
Enhance tiddler title for system tiddlers

Now the $:/ part of the name is rendered in grey, making the main part
of the title more prominent.

@tobibeer suggested this a long time ago; good idea!
More whitespace in core templates
Rejig plugins tab of control panel

Now we divide the plugins into categories and organise the displayed
information a bit better
Get ready for a new view template segment carrying information about plugins
Keep up-to-date changes for zh-Hant and zh-Hans
Fix problem with checking versions of plugins carrying a badly formatted "version" field
Add links to static representations for people with JS turned off
Refactor plugin loading to retain plugin info for all plugins

Previously we were not reading the plugin info for plugins that hadn’t
been loaded.
Add tiddler info "advanced" panel
Add Chinese translations for tiddler info 'advanced' panel
Add a class to tiddler frames in view mode

We’re already marking tiddlers in edit mode with tw-tiddler-edit-mode,
makes sense to make view mode tiddlers too.
Extend button widget to set text references

Previously the `set` attribute could only be used to identify a
tiddler, not a full text reference.