add Wechat SPP demo

1. add Wechat SPP demo using EasyCloud;
2. change Airkiss timeout to 60s, connect AP timeout to 30s;
3. fix Airkiss CM3 static lib.

NOTE:
1. use Airkiss to config device(connect AP);
2. send && recv message from wechat client:
     wechat   <===>  dev(USART)
Merge branch 'master' into remote_master

Conflicts:
	Projects/settings/Demos.wspos
change product_id/product_key  (short id)

use new short product id.
fix:  add topic length to msg recv callback

[fix]
add topic length to msg recv callback, when need to reply to the
sender(topic).

[udate]
EasyCloudService lib to v0.2.4:
1. pass topic length to msg recv callback, because topic data is not
null-terminated string, to fix topic incorrect bug.
2. set max MQTT message payload size to 512bytes.