templatekw: pass templater to _showlist() by an explicit argument Prepares for switching to the (context, mapping) API.

hgweb: make templater mostly compatible with log templates Prepares for gradually switching templatekw.showsuccsandmarkers() to new API. This was a PoC showing how to reuse templatekw functions in hgweb. We could remove rev, node, author, etc. from the commonentry() table, but we'll have to carefully remove all corresponding symbols from webcommands.*(). Otherwise, we would face the issue5612. Still templatekw.keywords aren't exported. Otherwise some tests would fail because the atom template expects {files} to be empty in filelog, but templatekw.showfiles() provides the {files} implementation.