Enable "open in new tab" for prettyLinks

[YakovL]

This set of changes introduces a helper for getting permalink/permaview url (Story.prototype.getPermaViewHash) and adds href attribute to prettyLinks so that right click works with them like with usual links and one can select "open in new tab" action

[YakovL]

Although one may also expect ctrl+click to work as "open in a new tab", I'll postpone introducing such behavior due to the following complications:

• not sure if that's a cross-browser behavior these days and what else may be expected to cause this
• same (may be a bit simpler) for MacOS (cmd+click? in all browsers? does e.metaKey catch cmd+click?)
• toggling also uses ctrl/meta (cmd?) key, to be decided whether opening in a new tab should only work when toggling is disabled (chkToggleLinks) (by the way, the logic whether to toggle seems to be rather weird)

I also don't expect one would need to disable adding href, but if that's the case, getTiddlerLinkHref can be overwritten (in the simplest case with getTiddlerLinkHref = () => 'javascript:;'