Add a command to strip source information from po files

[jnavila]

This is required in order to submit a po file, checked by git-po-helper, but no simple command is provided to format the po files as expected.

By the way, I may be also interesting to force a certain line break policy in po file, in order to not generate spurious diffs.

[jiangxin]

Add new options to git-po-helper update command:

• Update and remove location but keep filename, use:

  git-po-helper update --no-location zh_CN
  

• Update and remove both file name and location, use:

  git-po-helper update --no-file-location zh_CN
  

See PR #23