Change the download url and fix some nits reported by pylint

The download url is changed. See https://download.01.org/crosswalk/releases/.
Besides, fix some coding style issues reported by pylint.
Merge pull request #23 from yongsheng/downloadurl

Change the download url and fix some nits reported by pylint
Fix the flag '--version' not working when the folder 'xwalk_app_template' exists
The script won't download the build tool when the folder 'xwalk_app_template' exists.
After this fix, we can switch between versions more easily.

Solution:
1: If '--version' specified for make_webapp.py
   1) If we have previously downloaded the version,
      Replace xwalk_app_template to the version
   2) If not downloaded, download it
2: If no '--version' specified, use previous one
BUG=#24
Merge pull request #25 from kurli/tools_version_control

Fix the flag '--version' not working when the folder 'xwalk_app_template' exists
Why: Increase number of sample apps.
What: All 19 apps from 01.org.
How:
  Cloned from upstream repositories, from master branch without patching.
  Added single step script to build and package into xpk and apk.
  Requires make_webapps.py to be run first (in order for the android tools
      to be installed), then :
  $ ./make_01_webapps
      and wait.
  Apks and Xpks are put in apks/ and xpks/ appropriately.
Dependencies:
  git+bash : <http://git-scm.com/downloads>
  node+npm : <http://nodejs.org/download/>
Inhereted from make_webapps.py:
  python : <http://www.python.org/download/>