scalar: alphabetize and simplify config

scalar: alphabetize and simplify config

The config values set by Scalar went through an audit in the previous
changes, so now reorganize the settings and simplify their purpose.

First, alphabetize the config options, except put the platform-specific
options at the end. This groups two Windows-specific settings and only
one non-Windows setting.

Also, this removes the 'overwrite_on_reconfigure' setting for many of
these options. That setting made nearly all of these options "required"
for scalar enlistments, restricting use for users. Instead, now nearly
all options have removed this setting.

However, there is one setting that still has this, which is
index.skipHash, which was previously being set to _false_ when we
actually prefer the value of true. Keep the overwrite here to help
Scalar users upgrade to the new version. We may remove that overwrite in
the future once we belive that most of the users who have the false
value have upgraded to a version that overwrites that to 'true'.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>