Blob edit commit and continue editing button.

Fix http://feedback.gitlab.com/forums/176466-general/suggestions/6171315-add-button-on-blob-edit-page-to-save-continue-ed, analogous to AMR http://feedback.gitlab.com/forums/176466-general/suggestions/5900530-add-button-on-wiki-edit-pages-to-save-continue-e but for blobs instead of wiki.

![screenshot from 2014-08-13 13 31 23 continue editing button](https://cloud.githubusercontent.com/assets/1429315/3904774/cae7b610-22dd-11e4-8d58-4bf0e0877437.png)