Add environment variables for locating plugins

Start of fixing #531 (we still need to deal with
TIDDLYWIKI_EDITION_PATH)
Add support for TIDDLYWIKI_EDITION_PATH
Docs for environment variable support

Fixes #531
Remove extraneous tag

Tiddlers tagged “resources” show up in the Community tiddler, which we
don’t want here.
Refactoring plugin loading on Node.js
Allow arbitrary fields in plugin.info files

Fixes #642
Fixes undefined loop variables (fixes #657)
Add editor type mappings to control panel
Refactor codemirror plugin

It no longer overrides the edit-text widget. Instead we use the editor
type mappings to select which content types should be handled by which
editor.
Docs tweak
Merge pull request #658 from csugden/patch-1

Fixes undefined loop variables (fixes #657)
Update chinese translations
* for adding editor type mappings to control panel
Fixed problem with Markdown image handling
Merge pull request #659 from BramChen/master

Update chinese translations
added triple double-quotes delimiters for marco/widget parameters (to support json strings)
Docs updates
Refactoring for hygeine
Merge pull request #660 from buggyj/jsonparams

added triple double-quotes delimiters for marco/widget parameters (to su...
Docs update
added missing regex update for triple double-quotes macro params