Restore visibility of system tags in view template

On discussion at Hangout #38 we felt that hiding them was confusing,
and that there were few situations where a user would see system tags
except on system tiddlers.

core/ui/ViewTemplate/tags.tid

@@ -1,4 +1,4 @@
 title: $:/core/ui/ViewTemplate/tags
 tags: $:/tags/ViewTemplate
 
-<div class="tw-tags-wrapper"><$list filter="[is[current]tags[]!is[system]sort[title]]" template="$:/core/ui/TagTemplate" storyview="pop"/></div>
+<div class="tw-tags-wrapper"><$list filter="[is[current]tags[]sort[title]]" template="$:/core/ui/TagTemplate" storyview="pop"/></div>