On the 'tags and heads' view, add an option to enable or disable
'Sort refs by type'. This option is read from and written to the
config file. Clicking on the option will update the refs in the
view.

Signed-off-by: Michael Rappazzo <michael.rappazzo@infor.com>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>

In the 'tags and heads' view, the list of refs was globally sorted,
which caused the local ref list to be split around other ref list types.

This change re-orders the view to be: local refs, remote refs, tags,
and then other refs.

Signed-off-by: Michael Rappazzo <rappazzo@gmail.com>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>

This output was added in d93f1713b0 ("gitk: Use themed tk widgets",
2009-04-17), we can assume, by accident.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>