gitweb: Allow configuring the default projects order and add order 'none'

gitweb: Allow configuring the default projects order and add order 'none'

Introduce new configuration variable $default_projects_order
that can be used to specify the default order of projects on
the index page if no 'o' parameter is given.

Allow a new value 'none' for order that will cause the projects
to be in the order we learned about them. In case of reading the
list of projects from a file, this should be the order as they are
listed in the file. In case of reading the list of projects from
a directory this will probably give random results depending on the
filesystem in use.

Signed-off-by: Frank Lichtenheld <redacted>
Acked-by: Petr Baudis <redacted>
Signed-off-by: Junio C Hamano <redacted>