Add a add photo Button when user is in limited photo mode

[ruby109]

Add a add photo Button when user is in limited photo mode
当用户在限制图片的权限模式下，显示一个加号按钮，让用户调起 PHPicker 来选择新照片，仿新浪微博的设计

[longitachi]

滑动选择的两处bug，-1 修改为 -self.offset

var i = beginIndexPath.row
while (minIsBegin ? i <= maxIndex : i >= minIndex) {
    if i != beginIndexPath.row {
        let p = IndexPath(row: i, section: 0)
        if !self.arrSlideIndexPaths.contains(p) {
            self.arrSlideIndexPaths.append(p)
            // let index = asc ? i : i - 1 修改为 let index = asc ? i : i - self.offset
            let index = asc ? i : i - self.offset
            let m = self.arrDataSources[index]
            self.dicOriSelectStatus[p] = m.isSelected
        }
    }
    i += (minIsBegin ? 1 : -1)
}

for path in self.arrSlideIndexPaths {
    // let index = asc ? path.row : path.row - 1 修改为 let index = asc ? path.row : path.row - self.offset
    let index = asc ? path.row : path.row - self.offset
    ...

[longitachi]

Add a condition: showAddPhotoCell.
设置不显示cameraCell且非limited权限下，升序排列时候会有显示addPhotoCell的bug

[ruby109]

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