Import projects from Google Code.

Resolves #1257.

Issue import logic almost entirely taken from https://gitlab.com/o9000/google-code-to-gitlab ( ♥ @o9000).

### To do

- [x] List projects from Google Takeout file
- [x] Import Git repository
- [x] Import issues
- [x] Link to correct attachment URL (https://code.google.com/p/support-tools/issues/detail?id=50)
- [x] Handle deleted attachments
- [x] Handle blockedOn attribute
- [x] Add directions on how to get data from Google Takeout

### Import instructions

![Screen_Shot_2015-04-03_at_16.02.21](https://gitlab.com/gitlab-org/gitlab-ce/uploads/4a87038035fbad9441cf613b8cdcc690/Screen_Shot_2015-04-03_at_16.02.21.png)

### Imported issue

![Screen_Shot_2015-04-03_at_16.25.49](https://gitlab.com/gitlab-org/gitlab-ce/uploads/b2c2eaf5ecfcf57b3c48511eb5d26db4/Screen_Shot_2015-04-03_at_16.25.49.png)

See merge request !471