== Admin change list view customization with ListColumn ==

Related ticket: #8054 Move method properties for admin list customisation to ModelAdmin

This ticket adds:

 * beatifull API to admin change list customization

 * ability to customize and localize 3rd-party application without fork it

 * ability to apply custom template filters on field value or model method returned value without any magic

 * ability to specify witch field will be used in order for column based on model method


==== ListColumn API ====

Arguments:

 * field_name - model field or model method name

Keyword arguments:


 * header - change list column header. If not provided standard algoritm to header column calculation will be used.

 * filter - template filters will be apllied to value on output.

 * load_filters - list of required template tags libraries. This libraries will be load before apply template filters to output value.

 * order_field - specify witch field will be used to prowide order by this column.

 * value_map - choices used to mapping display value

==== Example ====

Current way to admin change list view customization:

{{{
class Account(models.Model):
    foo = model.BooleanField(...)
    bar = model.CharField(...)
    baz = model.CharField(...)
    bonk = model.CharField(...)
    ends = models.DateTimeField()

    def get_bar_column(self):
        return ...
    get_bar_column.allow_tags = True

    def timeuntil_ends():
        return ...


class AccountAdmin(admin.ModelAdmin):
    list_display = ['foo', 'get_bar_column', 'baz', 'bonk', 'timeuntil_ends']

}}}

Proposed way:

{{{
class Account(models.Model):
    foo = model.BooleanField(...)
    bar = model.CharField(...)
    baz = model.CharField(...)
    bonk = model.CharField(...)
    ends = models.DateTimeField()

    def get_bar(self):
        return ...

class AccountAdmin(admin.ModelAdmin):
    list_display = [
        admin.ListColumn('foo', header='Foo Description', filter='boolean'),
        admin.ListColumn('get_bar', filter='safe', order_field='bar'),
        'baz',
        'bonk',
        admin.ListColumn('ends', filter='timeuntil', header="Ending in")
    ]

}}}