Add device entity files;
1. Add unit test cases;
2. Add device test core file;
Merge branch 'master' into dev
1. Add test case;
2. Update travis run script;
Update install dependencies;
Install requests first;
1. Add message test cases;
2. Update payload;
1. Fix python 3 version issues;
2. Modify message test case;
1. Modify device tag/alias/registration_id entity name to avoid conflicting with push namespace;
2. Add device example;
1. Update python client version;
2. Fix device import error issue;
Modify the way to import device module;
Add device api sample;
Add tags server sample;