Translate "Einzelpreis" to "Single price"

In the "Profit Margin" report. We suggest to translate "Einzelpreis" to "Single price".

Steps to reproduce

1. Navigate to "Reporting > Projects > Profit Margin. Click on "Submit" button.
2. Click on any "details" link
3. One of the column title reads "Einzelpreis". Expected result is the English wording "Single price". That View is located at /admin/structure/views/view/report_details_view_billables/edit

Contributing patch

We're contributing a patch. I will attach it here shortly.

Using

• ERPAL: 7.x-2.1+38-dev
• Drupal: 7.39
• Debian: Wheezy 7.8 (64-bit)
• Apache: 2.2.22
• MySQL: 5.5.44-0+deb7u1
• GD library: 2.0.36
• jQuery Update: jQuery 1.8.2 and jQuery UI 1.10.2
• PHP memory limit: 256M
• Multilingual: i18n modules 7.x-1.13. With path www.domain.ext/en/ and www.domain.ext/fr/
• Firefox / Iceweasel: 38.2.1 (64-bit)
• Chromium: Version 37.0.2062.120 Built on Debian 7.6, running on Debian 7.9 (281580) (64-bit)
• Chrome: 45.0.2454.93 (64-bit)

Notes

Francewhoa, notes to myself

• In the following screencast the same column title is display in English at https://youtu.be/5LhUvcnhQ3M?t=14m26s