gitk: Implement a user-friendly Edit View dialog

gitk: Implement a user-friendly Edit View dialog

Originally gitk required the user to specify all limiting
options manually in the same field with the list of commits.
It is rather unfriendly for new users, who may not know
which options can be used, or, indeed, that it is possible
to specify them at all.

This commit modifies the dialog to present the most useful
options as individual fields.  Note that options that may
be useful to an extent, but produce a severely broken view,
are deliberately not included.

It is still possible to specify options in the commit list
field, but when the dialog is reopened, they will be extracted
into their own separate fields.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>