workaround for copying properties in ios8

**Problem:**
crash on iOS8

```
Thread : Crashed: com.apple.main-thread
0  libobjc.A.dylib                0x00000001989810bc property_getName
1  Chuze                          0x00000001001ba944 -[NSObject(NSPropertiesCoding) encodePropertiesWithCoder:] (NSObject+SFPropertiesCoding.m:23)
2  Chuze                          0x000000010003f890 -[CHBaseObject encodeWithCoder:] (CHBaseObject.m:64)
3  Foundation                     0x000000018cf73e30 _encodeObject + 1244
4  Foundation                     0x000000018cf7536c -[NSKeyedArchiver _encodeArrayOfObjects:forKey:] + 468
5  Foundation                     0x000000018cf75aa0 -[NSArray(NSArray) encodeWithCoder:] + 212
6  Foundation                     0x000000018cf73e30 _encodeObject + 1244
7  Chuze                          0x00000001001ba9bc -[NSObject(NSPropertiesCoding) encodePropertiesWithCoder:] (NSObject+SFPropertiesCoding.m:29)
8  Chuze                          0x000000010003f890 -[CHBaseObject encodeWithCoder:] (CHBaseObject.m:64)
9  Foundation                     0x000000018cf73e30 _encodeObject + 1244
10 Foundation                     0x000000018cf7536c -[NSKeyedArchiver _encodeArrayOfObjects:forKey:] + 468
11 Foundation                     0x000000018cf75aa0 -[NSArray(NSArray) encodeWithCoder:] + 212
12 Foundation                     0x000000018cf73e30 _encodeObject + 1244
13 Chuze                          0x00000001001ba9bc -[NSObject(NSPropertiesCoding) encodePropertiesWithCoder:] (NSObject+SFPropertiesCoding.m:29)
14 Chuze                          0x000000010003f890 -[CHBaseObject encodeWithCoder:] (CHBaseObject.m:64)
15 Foundation                     0x000000018cf73e30 _encodeObject + 1244
16 Foundation                     0x000000018cf7b5cc +[NSKeyedArchiver archivedDataWithRootObject:] + 192
17 Chuze                          0x000000010002fe4c -[CHLoginManager saveSession] (CHLoginManager.m:123)
18 Chuze                          0x0000000100023234 -[CHAppDelegate closeAppActions] (CHAppDelegate.m:192)
19 UIKit                          0x000000018f4c5d70 -[UIApplication _handleApplicationSuspend:eventInfo:] + 692
20 UIKit                          0x000000018f43d2b8 -[UIApplication handleEvent:withNewEvent:] + 1784
21 UIKit                          0x000000018f43cab8 -[UIApplication sendEvent:] + 104
22 UIKit                          0x000000018f4a902c _UIApplicationHandleEvent + 672
23 GraphicsServices               0x000000019205b504 _PurpleEventCallback + 676
24 GraphicsServices               0x000000019205b030 PurpleEventCallback + 48
25 CoreFoundation                 0x000000018c433040 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 56
26 CoreFoundation                 0x000000018c432fa0 __CFRunLoopDoSource1 + 444
27 CoreFoundation                 0x000000018c4311c4 __CFRunLoopRun + 1620
28 CoreFoundation                 0x000000018c371dd0 CFRunLoopRunSpecific + 452
29 GraphicsServices               0x0000000192059c0c GSEventRunModal + 168
30 UIKit                          0x000000018f4a2fc4 UIApplicationMain + 1156
31 Chuze                          0x000000010002256c main (main.m:16)
32 libdyld.dylib                  0x0000000198f6faa0 start + 4
```

**Description**
There are several new properties/methods in iOS8, which leads to crash.

http://www.redwindsoftware.com/blog/post/2014/08/20/NSObject-has-some-new-properties-in-iOS-8.aspx

**Suggested workaround** 
To exclude these properties from encoding/decoding.
Tested on iOS8.0, iOS7.


Anyone has better / more accurate idea?