Tentative reworking of GettingStarted

See this thread for background:
https://groups.google.com/d/topic/tiddlywiki/sDWP4NPe8XE/discussion

Translators: please don’t translate this material until it’s settled
down
Fix checking for non-empty folders in initcommand
allows to style buttons as though internal links

by assigning class="tc-btn-invisible tc-tiddlylink"
Disable links when transcluding caption field in toc macro

@BramChen does this work for you?
Typo
Translation of the TabsMacro and related samples for the fr-FR edition.

While we are at it, propose an addendum
at the end of the TabsMacro documentation
Adjust field and has filter handling of missing tiddlers

Now `[!field:name[value]]` and `[!has[name]` will treat missing
tiddlers as not having the specified field
Merge remote-tracking branch 'upstream/master' into fred
Remove dependency on overriding the core toc macro

Thanks to 5b38c21a417d2e5e2b85aed8010c88af32420e24
and a subsequent suggestion from @BramChen
Get rid of GettingStarted tabs in empty

I feel that we should keep empty.html’s GettingStarted very simple, and
link to other places for tutorial material
Add one-character macro names for every punctuation shortcuts

Per @evolena neat suggestion: <<:>> is shorter and looks better than <<dp>>
Translation in French of the documentation tiddler Tagging
Move the title display into a macro so that it can be overridden
Extension of the idea of 5b38c21a417d2e5e2b85aed8010c88af32420e24
Merge pull request #1221 from xcazin/timeline

Move the title display into a macro so that it can be globally overridden
Updated translations for Danish

Thanks to Birthe C
Merge remote-tracking branch 'upstream/master' into fred
Remove dependency on core timeline macro by overriding timeline-title() instead

In application of #1221
Merge pull request #1224 from xcazin/fred

Various updates to the fr-FR edition
fixes #1010

safe / sequential replacing of formatstrings for date conversions

please review & test
fr-FR translation for three introductory tiddlers on Filters.