Permit plugin-x plugins to ship third-party libraries.

Ignoring the libs directory's .jar files is strange. I'm not sure
whoever put the total block over libs/ knew that this is the standard
Android library directory and not just for NDK-compiled assets.

More granular ignores over libs/ contents would be better in the
future, but this fixes the odd sdk/ directory hack plugins currently
use and lets the Android build system auto-link libraries that're
shipped with plugins instead of forcing Cocos developers to manually
sift through a plugin's Android dependencies and include them by hand.
Modify the cpp template & tests to support compiling wp8-xaml & win8.1-universal project by console.
externals: using v21
Merge pull request #9126 from ricardoquesada/v21_externals

externals: using v21
ooops

commited by mistake debug messages
Using std::swap instead of CC_SWAP

CC_SWAP is deprecated. Use `std::swap` instead.
Merge pull request #9134 from ricardoquesada/std_swap

Using std::swap instead of CC_SWAP
[AUTO][ci skip]: updating cocos2dx_files.json
Merge pull request #9135 from CocosRobot/update_cocosfiles_1416159132

[AUTO][ci skip]: updating cocos2dx_files.json
Merge pull request #9108 from nilium/v3-plugin-libjars-unignore

Permit plugin-x plugins to ship third-party libraries.
Update CONTRIBUTE.md
Update the reference of submodule cocos2d-console.
Merge branch 'v3' into support-wp8
Merge pull request #9137 from natural-law/support-wp8

Modify the cpp template to support win8.1-universal project.
Merge commit '70fdf6af5d2b04972eb12872c1bcc2c8308ab3c8' into v3