Update the Snow White theme to use px for dimensions instead of em

The old behaviour meant that resizing the base font resized every page
element in proportion. The new behaviour makes the text resize within a
fixed layout, so that one can alter the number of characters displayed
on each line of a tiddler. The old behaviour can usually be emulated by
using the browser page zoom tool.
Ensure getTiddlerList() returns a copy of the tiddler list

Fixes #155
cla-individual draft ok
cla-individual and cla-entity draft for discussion
Fix broken regexps

Using .|\n was a very bad idea, as it doesn't match other newline
characters
Fix untagged tiddler list to exclude tiddlers which are being used as tags
Roadmap clarification
Update HTML5 saver to use current filename where possible

Most browsers still ignore the specified filename, sadly.
relative link to contributing.md
relative link to both cla's contributing.md
Fix problem with lowercase drive letters when saving with TiddlyFox under Windows
moving Harmony project attribution to contributing.md. contributors need to add there github name. entities need to add  entity info
removed external links from the CLA text, since links may break.
reversed contributing.md, since it will be created automatically. Use the Contributing.tid instead. Minor tweaks to CLA's
Improve comments
Fix expected test results for eachday filter operator

The tiddler "a fourth tiddler" doesn't have a modified date, and so
shouldn't appear
Fix eachday and sameday filter operators

There was some inconsistency of UTC vs. timezone handling
added Unamesa Association as (We or Us). Got OK from Jermolene to use CC-BY for media content.
Merge pull request #161 from pmario/activate-clas

First pass at a Contributors License Agreement (thanks to @pmario)
Rebuilt contributing.md